Tony: Well you see we're studying the eating habits of various vanishing cultures. For example, someone is talking about the Kikuyus of northern Kenya. And my roommate is doing the Cree Indians of Saskatchewan. And my professor suggested I do a slide show on us.

Harriet: Us?

Tony: The WASPs. Of northeastern United States.

--From "The Dining Room"

AMERICAN SOCIETY may be the great melting pot, but the American theater has always had a strong ethnic bias. Eugene O'Neill explored the brooding contradictions in the Irish-American. Clifford Odets celebrated the Jewish immigrant. Preston Jones was the bard of the Texas redneck and Tennessee Williams still has a corner on the southern degenerate.

A.R. Gurney writes plays about WASPs, mostly of the New England variety, a calling that is more or less tipped off by the blue pin-cord suit, the club tie and the button-down oxford cloth shirt he is wearing this particular afternoon, in defiance of the rising temperatures outside. After more than 25 years at his craft, Gurney, like the WASP culture he profiles with wit and perspicacity, has suddenly broken into the open.

His dexterous chronicle of a whole way of life as symbolized by a day's activities in "The Dining Room" has turned into one of the surprise hits of the Off-Broadway season. On Thursday, a Washington company opens in the Eisenhower as part of the six-play series the Kennedy Center is co-producing with CBS. Meanwhile, Gurney is readying a new play, "What I Did Last Summer," for a pre-Broadway tryout on the straw-hat trail, while a third, "The Middle Ages," is earmarked for New York production in the fall.

The wave that swept Reagan into the presidency, landed "The Official Preppy Handbook" on best-seller lists, and rehabilitated Bermuda shorts also seems to have benefited the modest playwright, who once observed that "WASPs don't go to the theater, it's too messy. They stay home and watch 'Masterpiece Theatre' instead." But if all of a sudden he is hot professionally, Gurney is otherwise true to the heritage of WASPdom, which prizes the cucumber as a model of cool. "I've written pretty steadily since 1956," he observes, "and while there has always been some feedback--someone somewhere saying what I was doing was valuable--I've never had great critical success in New York until now. Because I'm 52--no, I'm not, I'm 51--it's kind of nice to have a payoff."

That's about the only toot you'll get out of Gurney's horn, although he is gratified that WASPs finally seem to be coming out of the closet, after pretending for several decades to be "simply bland Americans." "I once said that I've always felt as if I were writing about a 1957 Chevy. By that, I mean that things become valuable, or we look at them as being valuable, only when they're obsolete," he reflects. "WASPs do have a culture--traditions, idiosyncracies, quirks, particular signals and totems we pass on to one another. But the WASP culture, or at least that aspect of the culture I talk about, is enough in the past so that we can now look at it with some objectivity, smile at it, and even appreciate some of its values. There was a closeness of family, a commitment to duty, to stoic responsibility, which I think we have to say, weren't entirely bad." That awareness tempers Gurney's satire: "Notice we don't dress everyone in the cast in pinks and greens with alligators on their shirts."

A product of the tightly knit world he profiles, Gurney was born and raised in Buffalo, acquired his constant nickname (Pete) at an early age, was packed off to private school and got the proper degrees from Williams College and the Yale School of Drama, where he once carried spears on stage alongside Kennedy Center producer Ralph Allen. There are still traces of the preppy in his pleasantly battered face, although when he laughs, he can look rather like Mel Brooks.

More than just an astute observation of evolving WASP mores, "The Dining Room" is something of a technical tour de force. Using only six actors, who play a multitude of roles from rambunctious 5-year-old tots to curmudgeonly grandparents, its overlapping scenes begin with a real estate agent showing the house early one morning, pass on to meals and between-meal revelations, and end up in the evening with an idealized dinner party. Each scene takes place later in the day, although not necessarily in the same decade, so that 10 a.m. in 1930 is followed by 11 a.m. in 1960, then, say, noon in 1980.

Not the least of his characters is the dining room itself, once the bastion of middle-class affluence that has slowly ceded its lofty position in the American house to the all-purpose family room or modernistic "eating areas." "I didn't realize this until I was in the process of writing," Gurney says, "but the dining room was the place where tribal lore, knowledge and manners were passed on. It was the place where the family gathered and traditions were either imposed or challenged. Unlike some cultures, where the issue is who eats what and how much, in the WASP culture it has always been how you eat and what you say while you're eating that counts. The dining room was a kind of courtroom for the middle-class family."

He suspects, also in retrospect, that it was his decision to install a wood-burning stove in the dining room of his own Victorian frame house in Newton, Mass., and turn it into a winter living room that triggered his concern. "I must have missed it," he says. "I was writing a totally different play and it kept wanting to be set in the dining room. I thought to myself, 'This is ridiculous--how can you have all these people sitting down, some of them with their backs to the audience.' But the scenes didn't seem to want to take place anywhere else."

"What I try to suggest in the play is that dining rooms require two things which we no longer have today. First, they required servants. There was always a swinging door into the kitchen and the assumption was that the process of preparing food, all the labor, was of no concern of those who were sitting around the table. And the second thing that the traditional dining room required was a woman to preside over it, a kind of idealized hostess who is simply a hostess and is willing to spend all that time organizing the seating, seeing the silverware is polished, arranging a social life. Women tend to refuse that role today. In my play, there's a maid who rebels early on, the women bring typewriters into the dining room, and the men are forced to accommodate a kind of non-dining-room world. So the play is not just about the decay of a certain way of life, but it's also about woman refusing her traditional roles as laborer and icon."

Far from interesting "about 50 people in New York on the East Side," as Gurney firmly predicted when "The Dining Room" opened at the Playwrights Horizon in New York last fall, the work seems to have tapped an audience long overlooked by the theater. The limousines pull up nightly to the Astor Place Theater, where the play was recently transferred to meet the ticket demand. "At curtain call, people in the audience have tears in their eyes," says Remak Ramsay, who is featured in the New York production. "It's almost as if they're grateful that someone has actually written about them at long last."

Gurney downplays the autobiographical elements in the play, although he has drawn freely on his Buffalo childhood: the extended breakfasts, during which he squirmed to get to school, and his father ordered him to "enjoy the meal"; the family dinners at which each member was expected to take turns exchanging ideas "in a civilized way"; the holiday banquets when his grandmother was "sung to, courted and generally pacified" over the table by her four sons.

"But there was also a rigidity about mealtime that could be depressing," he recalls. "I went to boarding school and I remember coming home over the break, having read 'The History of the American Republic' and trying to argue that Roosevelt, rather than being a villain, was actually an excellent president. I was not allowed to touch on the subject. My father was a very civilized and gentle man, but he did dominate the table and that subject was non-negotiable. I do believe cultures have a half-life like molecules and one of the signs of decay is an intolerance for free exchange and the superimposition of one authority. Well, democracy in our home had already degenerated into a kind of dictatorship."

That theme also finds expression in Gurney's two most successful plays prior to "Dining Room." "Scenes From American Life," the work that established him in the early 1960s, traced the erosion of authoritarianism in WASP culture and the worrisome tendency of Big Brother government to step in and take up the slack. In "Children" he explored the the internal contradictions wracking a wealthy family during its traditional summer vacation on Nantucket. That drama was very nearly a WASP version of "The Cherry Orchard," except that Gurney's characters were ultimately too tenacious to let the family estate slip into the hands of interlopers.

Plays are only part of his life, however. For the past 20 years, Gurney has taught English at MIT, dutifully reserving each summer for his writing, just as he restricts himself to one glass of wine at dinner, jogs daily and keeps a careful count of the Merits he smokes. So regular has the schedule been that his "circadian clock starts reacting automatically when May 15 or 16 rolls around and the juices just start to flow." Last fall, he finally broke the pattern by taking a year's sabbatical in New York City. There, he is proud to say, his wife expanded her role "of feeding four hungry mouths" by working as a nutritionist with pregnant Spanish-speaking mothers in Harlem and Bedford Stuyvesant. Gurney himself planned to study classical Greek and teach ex-convicts basic reading, writing and spelling skills at the Fortune Society. He had brought along a manuscript of "The Dining Room," however, and in short order it zoomed from a staged reading to full-fledged hit. Success not only scuttled his plans for the year, but also set him wondering if he shouldn't take the big leap into full-time writing.

"What I'd really like to do is to indulge myself more now," says Gurney, for whom the height of indulgence tends to be eating the whipped cream off a dish of strawberries. "I'd love to take a year off, just hole up somewhere in Italy or France and goof off. I'm afraid I'd be incapable. I'm a pretty driven guy. Competitive. That's the final tragedy of being a WASP."

He smiles the Mel Brooks smile. "We always have to be useful."