BRITISH PLAYWRIGHT Simon Gray wants a scotch before he ponders the question. Earlier in the day, flew in from London and he has been in rehearsal most of the afternoon. The drinkis to alleviate the growing sysmptoms of jet lag.

Gray has written the adaptation of Molie re's "Tartuffe" (which began previews last night in the Eisenhower Theater) and he's been asked if he didn't experience some trepidation in the course of the project. As the author of such trenchant dramas as "Butley" and "Otherwise Engaged," Gray has a solid reputation as one of Britain's best dramatists. But Molie re is Molie re, after all, the comic glory of 17th-century France and, along with Shakespeare, one of the theater's immortals.

"By my calculation, it is now about 2 a.m. in London," Gray replies, "and I haven't had a drink yet." He takes a few swift gulps, lights up a cigarette, and finally turns his mind, which is a lively one, to the question.

"Trepidation? No. 'Tartuffe' is unquestionably a great classic. But I think great classics can be stolen from without doing them harm. I could never damage 'Tartuffe,' although it is very much in the cards that 'Tartuffe' could damage me. But once one has decided to do it, one has to live it through. There's no point in bowing continuously to Molie re."

Still, a couple of gulps later, Gray admits that he prefers not to call his work an "adaptation." He rejects "translation," too. Finally, he settles on "a variation on the theme of 'Tartuffe.' " Better yet: "An English variation on the theme of 'Tartuffe.' "

He has followed the basic story, of course, about a religious hypocrite who weasels his way into the bosom of a prosperous French family, and then sets out to appropriate its wealth, seduce the wife and marry the daughter, all under the nose of the foolish patriarch, Orgon, too blinded by devotion to realize what's happening. But Gray has cast out Molie re's rhymed verse for prose, pruned some of the lengthier speeches on the nature of men and true religion, and emphasized the darker strain in the fable.

"I don't think an English version, which follows Molie re impeccably, can succeed on the English stage," he says. "There are a number of plays within the play. And I wondered if it was not possible to find an English play, the source of which is Molie re, but the feeling of which is quite different. I was after almost a domestic tragedy. Well, tragedy is not quite the right word. Let's say that Orgon comes closer to the brink in my play. He's a wonderfully robust and comic figure in Molie re and, in a sense, he never changes. That's one of Molie re's jokes. I was curious to see if I couldn't make the relationship between him and Tartuffe more complex, although by that I don't mean richer or better. But I think that Orgon is in a state of utter bewilderment when Tartuffe presents himself. You might say Tartuffe becomes a focus for Orgon's madness."

Gray turned out the first draft in Paris, while holed up in an "appalling" hotel, recommended to him by Harold Pinter's agent. "It's a grand city for writers," he says. "I do a lot of my first and second drafts there. For one thing, I know no one there. For another, you can be sure of getting a cup of coffee or a drink at a cafe' at any time of night, which is marvelous if you want to work until 2 in the morning."

With director Brian Bedford, he thrashed out the second draft in a suite at the Mayflower Hotel in New York. And for the past 12 days, he has been at the Kennedy Center, polishing the script and doing a lot of "serious thinking" about the production. (One of the decisions, reached by him, Bedford and Kennedy Center producer Ralph Allen, was to fire George Grizzard from the lead role last week. Bedford now will play it.)

"Tartuffe is not an English figure," Gray muses. "That peculiar combination of successful religious hypocrisy and buffoonery--well, I know of no equivalent figure in English literature. Our religious madness is rooted very deeply in our belief in respectable institutions, rather than cults that spring up overnight. The play has a much more honored history in the United States. My guess about American society is that there is a sort of rootlessness that makes it particularly susceptible to hypocrites like Tartuffe. Americans really are convinced that there is immortality. They've just got to figure out how to get it. The assumption over here is that, a) if you extend the number of years you live, you are doing something important, which I doubt. And b), if you live long enough, you never may get around to dying at all."

"That," says Gray, emptying his glass, "I also doubt."