IT WAS WITH SOME amusement that Roland Dumas, an urbane lawyer who served as Foreign Minister under the Socialists, recently recalled the roiled and polarized political climate of France's last presidential campaign, in 1981. ''I know people in the liberal professions, friends of mine, who quit France, went to England or elsewhere after Mitterrand was elected,'' said Mr. Dumas, sitting in his smartly appointed office on the Quai de Bourbon hard by the wintry Seine. ''They thought the country was finished.''

Dumas managed an indulgent smile, then added, ''But the Soviet tanks did not come'' - as a senior adviser to then-President Valery Giscard d'Estaing had warned they would. Mr. Giscard d'Estaing himself predicted that if Francois Mitterrand came to power, ''It will be Communist order or Socialist disorder.''

Once again, France finds itself in the midst of a presidential campaign - the first round of voting is on April 24 - but this time in a profoundly altered state of mind. Having Socialists in control of the French state for the first time since the 1930's has proved to be a momentous experience, but not for the reasons the right prophesied seven years ago.

Five years of Socialist rule and now two in which the reins of government have been held in tandem by a Socialist President, Mr. Mitterrand, and a rightist Prime Minister, Jacques Chirac, have made France a ''normal'' nation, one that has smoothly executed a transfer of power from right to left and then halfway back again. Under Mr. Mitterrand, fearful demons have been exorcised, myths have been shattered, and the axis of French politics has shifted to the center. The result is that today, for the first time in the 30-year history of the Fifth Republic, a presidential election is not being fought on sharply etched ideological lines. Just two decades after the 1968 student upheaval that shook French society and ultimately drove Charles de Gaulle from office, leaders of the left and right have discovered the allures of consensus politics.

FRANCOIS MAURICE MITTERRAND, who has presided over this normalization of French politics, is already at the epicenter of a highly personalized, American-style election campaign. Even after seven years at the helm of state, he remains an enigmatic figure, and it is typical of him that for months he has held France in a state of suspense over whether, at the age of 71, he will stand for a second seven-year term. Signs large and small are proliferating that he will run; the President has lately lost considerable weight, for example, which signals, in the Gallic phrasings of one close observer, ''either a woman in his life or that he's running.'' And although his closest aides continue to maintain that he has not yet made up his mind, the President is widely expected to announce his candidacy next month.

All opinion polls now show the Socialist President would defeat his two main rightest opponents - the energetic Gaullist Mr. Chirac and the avuncular Raymond Barre, a Prime Minister under Mr. Giscard d'Estaing - in the second-round runoff. Mr. Mitterrand's popularity puts enormous pressure on him to run, particularly since the polls also show that the Socialists' probable fallback candidate, Michel Rocard, a former Agriculture Minister, would just narrowly defeat Mr. Chirac and would lose to Mr. Barre.

And yet ''Mitterrand pivots on ambivalence,'' observes Franz-Olivier Giesbert, author of an insightful biography on the President. Mr. Giesbert argues that this ambivalence reflects Mr. Mitterrand's central political obsession: to have free hands and room for maneuver, never to be tied down to one option.

During the last two years, Mr. Mitterrand has taken an utterly novel political situation and deftly turned it to his advantage. In March 1986, a Gaullist-led rightist coalition trounced the Socialists in parliamentary elections, winning the legislature but leaving in place a Socialist President whose term still had two years to run. France suddenly had a hybrid coalition government, with Prime Minister Chirac handling most day-to-day affairs and President Mitterrand acting as a kind of political referee while jealously watching over his constitutional perogatives as Commander in Chief of France's armed forces.

''Cohabitation'' - the coy expression for this fluid power-sharing arrangement - has demonstrated that the Fifth Republic constitution instituted by Charles de Gaulle in 1958 was more flexible than anyone had thought. It has also shown that the ''cold civil war'' between the left and the right which had characterized French politics since the aftermath of World War II has finally drawn to a close.

Since the war, the highly successful political strategy of the right-wing Gaullist party had been to confront the French electorate with a stark choice: either elect the right, or face a doctrinaire Communist Party. The result was that so long as the Communists held a stubbornly loyal fifth of the electorate, French politics was blocked -to the advantage of the right.

But today, as the presidential candidates crisscross the nation, one constant of postwar French politics is strikingly absent: no one is talking of the menace posed by the French Communist Party, because it has shriveled to the status of a leftist sect; its presidential candidate, a folksy figure named Andre Lajoinie, will do well if he gathers 8 or 9 percent of the popular vote in the first round.

By drawing the Communists into his first cabinets, where they held four minor portfolios before stomping out in disillusionment in 1984, Mr. Mitterrand was an architect of their destruction. The Communists were given little real power - the Socialists had a hefty parliamentary majority without them - and were neutralized as an opposition force. Mr. Lajoinie now ruefully admits that it was ''a mistake'' for the Communist Party to have entered the Government, thereby losing its status (Continued on Page 56) as France's main voice of the disaffected. (That role has now fallen to Jean-Marie Le Pen's ultra-right, anti-immigrant National Front.) With the Communists in eclipse and the Socialists now the nation's biggest party, France appears destined to be governed from the center. The winner of the presidential run-off vote on May 8 will probably be obliged to cobble together a shifting parliamentary coalition. The days of the imperial French presidency and rubber-stamp National Assembly appear to be numbered; the next president will almost certainly have to be as much an arbiter as a chief executive officer. IT IS HAZARDOUS TO TRY TO PIN-point a nation's mood, but, where French politics is concerned, a word that crops up repeatedly in conversation is desabuse - disillusioned, disenchanted, undeceived. For neither the left nor the right has demonstrated that it can cure France's economic malaise or make significant progress in reducing the ranks of two and a half million unemployed.

In 1981, the Socialist victory awakened hopes on the left for a major transformation of society, and Mr. Mitterrand's Government enthusiastically began to apply its 110-point program, the centerpiece of which was the nationalization of banks and other major industries. But France's go-it-alone attempt to jump-start its economy quickly collided with international economic realities, and by 1983 the Socialists were obliged to devalue the franc and apply belt-tightening measures.

After Mr. Chirac's Gaullist-led coalition won a parliamentary majority and took over in 1986, it started to denationalize what the Socialists had nationalized. But the crash of the American stock market and the tumbling dollar have limited the impact of its other ''liberalization'' measures. Andre Glucksmann, an iconoclastic philosopher and political commentator, noted that during the last few years his countrymen have realized that major events touching their existence keep happening outside France - be it the Wall Street crash or the superpower arms accord. ''This contributes to the national malaise,'' says Mr. Glucksmann.

Yet the loss of illusions - painful in such a proud and inward-looking nation - has been part of the normalization process. Alain Minc, an economist and author of several best-selling books, scratched a 360-degree circle on a notepad and observed that the next president might have a 10-degree margin of maneuver on the economy. ''You don't kill for 10 degrees of change,'' he said. ''In the next election it is not society that is at stake: it is simply a political choice.''

According to Mr. Minc, the beginning of a blurry convergence of views between the right and the Socialists, who appear to have abandoned any ideas of renationalizing industries, has meant a displacement of the right-left split in French politics away from economic questions and toward ''values'' - issues like immigration and justice. But ''these conflicts will surface very little in the campaign,'' Mr. Minc said. ''The campaign will be about personalities - in the American manner.''

AMAN OF GRADUAL, elegant conversions, Francois Mitterrand in many ways incarnates the turbulent political trajectory of France during the last five decades. Born into a well-to-do family in southwestern France, he served in the French Army and was captured by the Germans in World War II. After escaping from a German pris-oner-of-war camp, he briefly worked as a minor official for the collaborationist Vichy regime, but eventually joined the anti-Nazi Resistance. Mr. Mitterrand annually recalls his Resistance years by making a pilgrimage to Solutre, in central France, where as a young organizer in the underground he was hidden from the Gestapo.

In 1943, he traveled to Algiers to meet with de Gaulle, the leader of the Free French in exile; but an incipient personal rivalry kept him from rallying to the general's standard. A cabinet minister 11 times under the revolving governments of the postwar Fourth Republic, Mr. Mitterrand, on the left but fiercely anti-Communist, became one of de Gaulle's most determined foes. As the leader of the Socialist opposition, he ridiculed the general's independent nuclear force, the force de frappe, as a bombinette, or little bomb. But, since coming to office in 1981, he has stoutly defended it and consolidated France's unusual national consensus on defense matters.

The President clearly fascinates the French, who, even when they disagree with him, seem to admire his political adroitness and his mastery of the cadences and richness of the French language. ''Mitterrand is a seducer,'' said Jacques Amalric, foreign editor of Le Monde, ''and he has seduced France.''

In his serenity and unhurriedness, there is about the President an aura of the 19th century. ''I lived my childhood in another century,'' he once wrote, ''and it cost me an effort to leap into ours.'' When the President stands in public, he is utterly still, not shifting his feet or moving his arms. The Sphinx of the Elysee seems to defy others to find a chink in his emotional armor. He has a prodigious memory and at ceremonies where he bestows the Legion of Honor or other awards, speaks fluently and without notes about the lives and accomplishments of a half-dozen people arrayed before him. Important speeches given to the Bundestag in Bonn and the Knesset in Jerusalem have been eloquently delivered on the basis of notes sketched out at the last minute.

The President is absorbed by the subject of death and, on foreign trips, makes a point of visiting the cemeteries where famous statesmen and writers are buried. Yet there is something playful about him as well. He routinely slips out of the confines of the Elysee and walks around Paris with several plainclothes policemen. At night, he flees the palace for his apartment on the Left Bank.

Although he has spent most of his political career in Paris, Mr. Mitterrand is spiritually rooted in la France profonde - the France of the provinces. ''He is capable of saying things like, 'Every man should know the names of the trees,' '' observed Jean-Francois Fogel, a journalist and writer. ''That touches something in the French. He is a master of rhetoric, and the French adore rhetoric.''

For his foes, Mr. Mitterrand's great rhetorical gifts actually underline his biggest shortcoming. ''Mitterrand is a man whose action is always at the level of the verb,'' says Thierry de Montbrial, the head of the French Institute of International Relations and a partisan of Raymond Barre. ''If you ask me what he has actually done in his seven-year mandate it is very difficult for me to say.''

In fact, when asked this simple question, presidential aides draw up a modest list, usually starting with the fact that Mr. Mitterrand guaranteed the changeover of power in France, then pointing out that he abolished the death penalty, enacted measures to give France's regions greater self-government, liberalized television and consolidated the country's defense consensus.

THERE IS A Phoenix-like quality to Mr. Mitterrand's political career. Before his victory in 1981, he was twice defeated, in 1965 and then in 1974, as the left's presidential candidate. During the last two years, he has pulled off another astonishing comeback. After the Socialists' defeat in the 1986 legislative elections, the conventional wisdom had it that he was finished; journalists began writing about the ''apres-Mitterrand'' era.

Cohabitation saved the agile Mr. Mitterrand. With little day-to-day responsibility, the President positioned himself as a statesman and father-of-the-nation figure, high above the petty maneuvering of ordinary politicians. He took occasional rhetorical pot-shots at Mr. Chirac, the frantically activist Prime Minister, but avoided head-on clashes that would have diminished his presidential dignity.

And he emphasized his constitutional position as France's chief representative to the world and the commander of its armed forces. A typical bit of television footage recently found him on the command deck of the aircraft carrier Clemenceau off Djibouti, declaring that France would not withdraw from the Persian Gulf.

Mr. Chirac, by contrast, was saddled with the unrewarding task of reviving the French economy: the two and a half million unemployed belonged to him, not to the President. It was an ideal situation for Mr. Mitterrand who, as his biographer Mr. Giesbert put it, ''became a kind of president of the opposition.'' His popularity soared.

Yet at the end of a second term, Mr. Mitterrand would be 78. According to those privy to his thinking, he has been sobered by the ravages of age on President Reagan and by the recent ouster of the half-senile Habib Bourguiba as President of Tunisia. Consumed by his own place in French history - he has an archivist working full time at the Elysee - he knows that if he steps down now he will leave gracefully. And the period after the election looks to be a messy one, particularly if it involves a re-elected Socialist President without a majority in the National Assembly.

Yet by stepping down, Mr. Mitterrand could clear the way not only for a rightist victory but also for acrimonious splits within his Socialist Party. The decades of work spent in rebuilding the Socialist organization into France's biggest party might be undone. It is uncertain, moreover, whether the Socialists, if defeated, would long embrace the tough defense policies that have been the hallmark of the Mitterrand era; in opposition, it is likely they would lurch to the left, as did the West German Social Democrats. Historians might accuse Mr. Mitterrand of sundering France's stern consensus on defense.

As he tours the country on precampaign sorties, Mr. Mitterrand is greeted by Socialist partisans who chant his nickname - ''Ton-Ton,'' or uncle - and hold aloft hand-written placards imploring, ''Don't abandon us, Francois!'' In Paris, a pro-Mitterrand designer has come up with $150 ''J'aime Ton-Ton'' silk shirts. Posters have begun to appear showing a Mitterrand-esque hand reaching down to a smiling baby, with the words ''Mitterrand Generation'' - linking the elder statesman in the Elysee to the youngest of French citizens.

Mr. Mitterrand is a curious object for this orchestrated cult of adoration. Stately, grave, remote, he is a solitary figure on the precampaign trail, rarely seen in the company of his wife, Daniele. He exists in the public imagination as a man alone.

MITTERRAND HAS two ambitions simultaneously,'' said Dominique Jamet, a conservative journalist who has joined a group of French intellectuals lobbying for a second term. ''To be president -and to retire and write and think.'' It seems a classic instance of the politician's famed ambivalence, but the President is clearly positioning himself to win a second term. Victory would bury the ignominy of the defeats of 1965 and 1974, and assure him a cherished place in the Pantheon along with the great French Socialist Jean Jaures, who shaped the Socialist Party before World War I. A Mitterrand campaign, say those close to him, would be short, consensual and focused on the President as a rassembleur, or rallier, of all Frenchmen. The emotive symbolism of the Socialist Party would fade into the >background. There will be no 110-point program to inspire, or frighten, the electorate. On sorties out of Paris, Mr. Mitterrand has already started appealing for an ''indispensable synthesis'' of left and right.

Mr. Mitterrand is not alone in casting himself as a rassembleur. Prime Minister Chirac, whose abrasive manner once earned him the nickname ''the Bulldozer,'' has summoned American-style commissions of ''wise men'' to pronounce on such double-edged issues as the media and immigration. And Mr. Barre, who imposed economic austerity on France when he was Prime Minister under President Giscard d'Estaing, has sought to humanize his own austere public persona by appealing for ''solidarity'' with the disadvantaged. The next French president will be the candidate who has stretched farthest across his side of the left-right divide.

When they invented ''cohabitation,'' the politicians were lagging behind ordinary Frenchmen, who have been coexisting amicably enough for years.

Since France pulled out of Algeria in 1962, the nation has truly been at peace for the first time in centuries. The erosion of smoke-stack industries and the emergence of a vast service sector have eroded class loyalties. Opinion pollsters find fewer and fewer Frenchmen willing to identify themselves as being ''of the left'' or ''of the right.''

The Communist Party's summons to Karl Marx's class struggle has long sounded tinny and archaic; the party's decline has been accompanied by a weakening of trade union allegiances and the fizzling of grandly trumpeted strikes.

FRANCOIS MITTERRAND'S France, normalized politically, stripped of its illusions, is not a particularly happy nation. It is a country edgy about its place in the world, fretting about the economic strength of West Germany, committed in rhetorical terms to building a more intimate comity of European nations but uncertain how, or whether, this will work. In film, theater and literature - realms in which it has traditionally excelled - France seems to be in a trough. There is talk about the exhaustion of the French imagination; a recent best-seller was suggestively titled ''La France Paresseuse,'' or ''Lazy France.''

Michel Jobert, a cagey veteran of past political struggles who served in the cabinets of both the Gaullist Georges Pompidou and the Socialist Mr. Mitterrand, mused one morning in his cluttered Paris office about the blandness of the presidential campaign. ''The ketchup that the candidates will propose to the voters will all have the same taste,'' said the wispy former Foreign Minister. The election itself, he argued, was not that important, but the period after it was.

''The French need a dream,'' Mr. Jobert said. ''We need to believe that France has perhaps a universal vocation, and we will need a lighthouse that will put out very simple messages. National independence, a nation that is the defender of human rights - these are the signs of our national identity. And if we do not have that we will have a little bit lost our way.''

Is Francois Mitterrand that lighthouse? In his 72d year, can this Florentine politician and rhetorician summon France to a common enterprise? The weeks and months ahead might begin to provide an answer -but they probably will not unlock the enigma of this most private of public figures.

Photo of President Mitterrand at ceremonial appearance at Arc de Triomphe, with Prime Minister Jacques Chirac (Patrick Durand/Sygma) (Pg. 33)