For the very first time in an acting career that began when she was a teen-ager, there is talk of an Academy Award for Jessica Tandy. ''It's lovely,'' the 80-year-old star of ''Driving Miss Daisy'' said the other day, her attentive, ascetic face suddenly lighting up in a girlish smile. ''This is by far the best movie role I ever had.''

''But let's not get our head too swollen,'' she continued. Miss Tandy seemed to be poised weightlessly on a flowered couch in a comfortable old mid-Manhattan hotel that is frequented by theater people and transient movie names. It has long been the pied-a-terre of Miss Tandy and her husband of 48 years, the actor Hume Cronyn.

The Oscar talk is driven by Miss Tandy's portrayal of Miss Daisy Werthan, an eccentric, highly independent Southern Jewish woman who ages from 72 to 97 during the film. More than four decades ago Miss Tandy achieved theatrical stardom with her acclaimed portrayal of another Southerner, Blanche DuBois, in the 1947 Broadway premiere of Tennessee Williams's ''Streetcar Named Desire.'' She went on to win a Tony Award for ''Streetcar'' (1948), and two more for her roles in ''The Gin Game'' (1979) and ''Foxfire'' (1983).

Just getting the part of Miss Daisy was a surprise, she said. ''I'm not a big movie name,'' she explained, ''and I knew they needed someone who was bankable. Certainly, in films, I've played small supporting roles for the most part.''

No Blood, No Thunder

''What has been happening to the film is remarkable,'' Miss Tandy continued, ''but there is something about the story that has allowed the play to run for years.'' The screen adaptation of Alfred Uhry's Pulitzer Prize-winning drama subtly reflects decades of postwar social change in the South, telling the story of the developing friendship between Miss Daisy and Hoke Colburn, her black chauffeur, played by Morgan Freeman.

''Driving Miss Daisy'' climbed to first place at the nation's box offices two weekends ago, passing ''Born on the Fourth of July,'' ''Tango and Cash'' and ''War of the Roses.'' Such acceptance may be surprising to the major film studios - every one of which turned the film down, some of them twice - since ''Driving Miss Daisy'' is a slow-paced, closely observed drama that, unlike its competition, is utterly devoid of blood and thunder. The film has already earned more than triple its modest $7.5 million cost.

Dana Ivey created the role of Daisy Werthan in the play, and Miss Tandy saw Frances Sternhagen in the role at the John Houseman Theater Off Broadway, where it is still running. Miss Tandy says she understands what it feels like to be replaced in a Hollywood production. Vivien Leigh was given her role as Blanche DuBois when ''Streetcar'' was adapted for the screen. Is It Good to Be Unbankable? ''I felt kind of bad, because everyone else in the play went into the movie 'Streetcar,' '' she said. ''And I guess that's how I got the idea I'm not bankable as a movie star. But I've always wondered if it wasn't a good thing. Instead of getting all those roles on the stage, maybe I'd have stayed in films, and been played out long ago.''

Miss Tandy has worked steadily in recent years, but without wide acclaim since her 1983 Tony Award. ''I suppose I feel rediscovered,'' Miss Tandy said after a pause. Her silver hair was tied back regally with a black silk ribbon above a black wool suit and beige Chanel blouse. The silver Paloma Picasso earrings she wore were an 80th-birthday gift from her movie co-workers last June on location in Atlanta.

''Driving Miss Daisy'' also stars Dan Aykroyd as Daisy's son Boolie, Patti LuPone as his wife, Florine, and Esther Rolle as Daisy's servant, Idella. In the film, the chauffeur is forced on Daisy after she crashes her new 1948 Packard in her neighbor's garden. ''Although Alfred told me the role is a composite of his grandmother and others in his family, in fact his grandmother did total the car,'' Miss Tandy said.

''I can imagine just how she'd feel,'' Miss Tandy said after a pause. ''I still drive - thank goodness!''

Smaller, Yes, but Not Slower

Age has barely slowed this actress who has four grandchildren and three great-grandchildren. ''It's taken its toll, though,'' she said with a laugh. ''I'm 5 foot 3 now, when I used to be 5 foot 4.''

How did she prepare for the role of a 72-year-old woman who ages 25 years during the film? ''It was very simple,'' Miss Tandy said. ''I'm in the middle of those ages. Luckily, I can still act like a vigorous 72-year-old!''

In preparing to play Daisy, Miss Tandy also talked with Mr. Uhry's mother about her memories of postwar Atlanta. And she worked with a dialect coach. ''The Atlanta accent was very difficult,'' she said. ''Actually, I hope I didn't slip too much.''

If she is associated with playing Southern women, ''it's only because I've had very good Southern parts,'' she said of roles like Blanche in ''Streetcar'' and Amanda Wingfield in Williams's ''Glass Menagerie.'' She has played women of every conceivable social class and regional origin in England and America in more than 150 major roles; she is no stranger, either, to playing the elderly in plays like ''Foxfire'' and ''The Gin Game'' and films like ''Cocoon.''

Miss Tandy agrees that Daisy Werthan is a complex character, ''a very spiky lady, fiercely jealous of her independence,'' she said, adding: ''She was the product of her time and she had the prejudices of her time. But she does grow. She learns. By the end of the film she's really changed. And you know, the whole world changed at the time.''

As depicted in the film, Miss Daisy is an extremely wealthy woman, but ''she has never forgotten her humble beginnings,'' said Miss Tandy, adding that she ''could relate to that.'' She explained: ''We had to watch all the pennies we had when I was a child.'' That was in London, where her father died of cancer when she was 12.

Getting Around Frugally

Miss Tandy said that Miss Daisy, in clinging to her memories of poverty, was ''not one of those people who needs more and more and more.''

''I think I have some of these characteristics,'' she said. ''I'm very frugal in some ways. I'm not one to have a stretch limousine. In New York I take the bus and the subway -because it's the quickest way to get around.''

Acting the role was ''physically tiring,'' she said, ''but when you're working, somehow you get the energy to do it.'' She said she kept remembering that for Daisy, ''even in the nursing home, where Daisy is down to her absolute basics, I don't think she would have given up. It's just that she suffered what we all come to as we get older - less ability, physically, to do things.''

She and Mr. Cronyn visited nursing homes when they were researching ''The Gin Game,'' Miss Tandy said, ''and I'll never forget it.'' Did it take courage for an 80-year-old to portray a character who becomes physically and mentally debilitated in her 90's? ''No, not courage - it's just all part of the human condition,'' Miss Tandy said. Nevertheless, the scenes after Miss Daisy has had a stroke were difficult for Miss Tandy. ''Those scenes were painful for Daisy, and therefore, painful for me. I know people who skip a beat now and then. I know how angry it makes them - they say a word and it's not the one they mean. It's frightening.'' She put her hand on her forehead and closed her eyes. ''At my age, I do wonder what my end would be,'' she said. ''I hope against hope it will be quick, and that I won't go through a long illness, or be a burden on people, and be mentally out of it. But of course you have no control over any of this. I don't know how much longer I can go on. And I do hope I have the sense to know when to stop.''

She looked at her interviewer, smiled, then said: ''But for now, the old motor is still turning over. Though the old motor is slowing down, that's for sure.''

''But I just constantly keep working,'' Miss Tandy continued. She would like to do another film, and a play - perhaps one with Mr. Cronyn - but ''I haven't the faintest idea what I'll do next.'' She paused, then said: ''Of course, whatever part they offer me, it's going to be an old lady!''