BANJUL, Gambia, Aug. 26— When Lieut. Yahya Jammeh seized power in this West African country in a bloodless coup last month, breaking one of the continent's longest traditions of electoral democracy, he joined the increasingly crowded ranks of soldiers who have risen to power in Africa.

From the start, Lieutenant Jammeh, 29 years old, fresh from a military-police training course in the United States, has promised that his would be a "coup with a difference." He has vowed that he and his fellow soldiers are "not here to perpetuate ourselves," and will return to the barracks "as soon as we have set things right."

Such pledges say much about this region's recent history. Young military officers have time and again overthrown larcenous or ineffectual civilian leaders in the name of national redemption, only to cling to power through violence while inflicting even greater disaster on their countries' economies. Donors Are Skeptical

So if ordinary people in a mostly illiterate population of mainly peanut farmers and poor city dwellers have applauded the coup and its leader, many educated Gambians are bracing for the worst. Their skepticism is shared by Gambia's major donors, the European Union and the United States, which have suspended most of their aid and have pressed for a quick return to civilian rule in the tiny former British colony that stretches along the Gambia River.

"This is exactly the same phenomenon we have seen elsewhere, with the only difference being that so far there has been no violence," a Western diplomat said of the coup.

For his part, the young lieutenant now in charge here bristles at the comparisons with nearby countries like Liberia, where a sergeant named Samuel K. Doe seized power in 1980 promising equality and an end to corruption. Instead, the country plunged into a civil war that continues today.

But even as he pledges to announce a timetable for a transition to democracy by the end of September, Lieutenant Jammeh, a child of the rural upcountry whose formal education ended in the 10th grade, complains that suspensions of vital donor aid in the meantime amount to "neocolonialism."

"We are here for reasons that are peculiar only to Gambia, and what has happened in other parts of the continent, that does not concern us," Lieutenant Jammeh said in an interview in a crimson-carpeted salon of State House. Political Activity Banned

Other Gambians, and several longtime political analysts here say that despite these protestations, the similarities linking the Gambia's new rulers to other military regimes in the region are disturbingly clear.

Governing by decree with four other junior officers and several civilians at his side, Lieutenant Jammeh has barred all political activity, arrested two socialist journalists who defied him, and detained many of his superiors in the 800-man armed forces, while confining ministers of the former Government to house arrest.

"Our fears and apprehensions are pretty much the same, because military governments are generally the same," said Kenneth Y. Best, the managing director of The Daily Observer, a Liberian citizen who was forced to flee the Doe regime's terror in 1990. Promises to Fight Corruption

Much like the early President Doe, Lieutenant Jammeh has said that his goal is to wipe out corruption and help improve living standards in a country where the illiteracy rate is 70 percent and per capita income is $300 a year.

The example the new leader uses most often to illustrate his country's backwardness is what he calls the failure of predecessor -- Sir Dawda K. Jawara -- to build a single hospital in 30 years.

A more telling case, some Gambians say, and one that may negatively affect the country's course for generations, is the deposed President's failure to build a university, or even, as some here tell it, a single new high school.

"We had elections every five years; I guess that was the legacy," said one former Government Minister who spoke on condition of anonymity. "It seems pretty clear now that we could have done a lot better. All we can do now is pray that these young fellows will know what to do."

Map of Banjul, Gambia