IF THEY ever make a movie about the writing of "Teibele and Her Demon," Isaac Bashevis Singer wants it to be called "only on Saturday."

Singer, who is 75, and collaborator Eve Friedman, who refuses to pinpoint her age beyond acknowledging that "so far as Isaac and I are concerned, it's definitely May and December," took three years of Saturdays to write their play -- what with his full schedule of fiction-writing, phone calls and public appearances, and hers of teaching English in a girls' high school in Manhattan.

In Washington last week to fine-tune and promote the play for its Arena Stage opening this Wednesday, Friedman accompanied Singer on his public rounds and acted the parts of escort, interpreter and interview subject.

Her role tended to encourage a first, wildly wrong impression of Singer as a literary legend in need of a nursemaid -- an impression complemented by his thick glasses, warm black sweater and navy blue suit several decades out of fashion. But his hearing betrays him -- it is perfect. And wherever else Singer's frailties may lie, they are not in his vocal chords. a question arouses a strong feeling, his answer strikes like a coiled snake.

"I believe in free will," he says when asked about the prominent influence of demons and other unearthly forces upon his characters. "But we only have control when we choose to have control. This is done with a great effort. With a deep strong decision. If we neglect to make a decision, we just flow, we just drift with life. We're all very lazy. We only do things if we are pushed, and the two great pushers are money and love."

In "Teibele and Her Demon," it is love that does most of the pushing. Alchonon, a widower dissatisfied with all the prospective wives the matchmakers have offered him, happens to overhear his neighbor Teibele (a shopkeeper who has been deserted by her husband but remains, technically, married) tell a yarn about a woman wooed by a demon. That same night, Alchonon slips into Teibele's bedroom identifies himself as the demon 'hurmizah, "ruler over darkness, rain, hail, thunder and wild beasts," and commands her to let him share her bed.

Most authors will do almost anything to avoid a capsule explanation of a substantial work, but Singer is perfectly happy to spell out the essential theme of "Teibele and Her Demon."

"This is a story about a man who had lust for a woman, and he felt that only by disguising himself as a demon can he get her," he says, arching forward on the low couch alongside Arena founder Zelda Fichandler's desk. "Of course, if this woman hadn't wanted to be deceived she would have realized who he really was. The deceiver and the deceived are loving partners. The passion to be deceived is even stronger than the passion to deceive. She wants to believe that she has suffered and loved a demon and not a nobody."

(The bawdy treatment of sex in Singer's fiction has always appalled the Yiddishists, the official keepers of the language and literary tradition in which he writes. "I'm a lusty ascetic," he says, "and let me tell you, all ascetics are lusty.")

Singer points out that he was employing supernatural forces long before they became fashionable. "I really like to write about demons," he says.

He has not seen any of the recent movies on the occult, but questions them. "You cannot make a movie about the supernatural," he says, "because the movie is actually a denial of the supernatural. You cannot photograph the soul, you can only photograph the body." In the theater, he hopes, supernatural comings and goings can have something like the hazy, mysterious quality he gives them in his stories.

"I have this belief that we are surrounded by great mysteries all the time," he says. "There are many things for which we have no evidence."

Suddenly, there is a message from overhead: "Sherwin Henry, please go to the Coke machine."

Singer twists around to identify the source of the interruption -- a loudspeaker mounted high on the wall. "For this voice," he says, "I have evidence."

Singer's pantheon of great writers contains one great temple devoted to the Russians (Tolstoy, Dostoevsky, Gogol, Chekhov), a large ancillary chamber for the French (Flaubert, DeMaupassant) and a miscellany room for such disparately dark authors as Strindberg and Poe. The English get a foot-locker for the poetry of Byron and Shelley; but there is no provison for English writers of fiction. Jane Austen is "good but completely dated," says Singer.

"But I'm not really an expert about literature," he adds. "Whatever I say is just my personal impression, and it may be completely false. All generalizations are false, and my generalizations are doubly false."

Growing up in Warsaw, the son of a rabbi, Singer scarcely ever saw a play. "My parents considered movies and theater all the work of Satan," he says. "They wanted me to study religion and the Talmud." When he did, infrequently, attend the theater in his 20s, the usual choice was between a French play -- "always a story about a man and a wife and a lover" -- or the Yiddish theater, which was "mostly about a little cantor who became a famous opera singer . . . and then a rich woman fell in love with him, but he said no, I will marry an orphan, and then he had a rich uncle who said, I will give you $100,000."

Even now, living half the year on New York's upper West Side in a cavernous old building called The Belnord at 86th Street and Broadway, Singer seldom goes to the movies, almost never to the theater, and reserves the television set for presidential elections. Every now and again, his wife Alma will turn the television on and scare Singer half out of his wits -- "when I open the door and hear there are strange men in the house."

Singer was, briefly, the second-string drama critic for the Jewish Daily Forward, where his fiction has appeared for decades. But the first string critic, who enjoyed the advantage of also being the editor, "knew beforehand what the good plays and what the bad plays were, and he went to all the good plays himself." In addition, his tickets were usually to second nights, and some of the plays already had closed by the time he got there. "It has really spoiled my view on the theater," he says.

Nevertheless, Singer says he always has wanted to write a play. "I knew that writing a play is the most difficult thing in the world, more difficult than writing a story or a novel or an essay. You have in two hours to give to people a real story of an incident that must have tension. Of course, to write a bad play is not much of a challenge."

"Teibele and Her Demon" is Singer's second experience in the theater. His first was unsuccessful 1974 adaptation of another short story. "Yentl the Yeshiva Boy." "On 'Yentl,'" says Singer, "I was given a collaborator. In this case I have chosen a collaborator."

We met at a literary reception in New York, where we just struck up a conversation," says Eve Friedman, a friendly but forceful-looking woman who is studying the awkward business of being a Nobel Prize winner's unknown associate. After their meeting in 1973, Singer and Friedman went to lunch and talked. Friedman talked about the plays she had written -- several of them produced in universities and off-off-Broadway -- but "I had no thought on my own of suggesting that we work on a play together," she says. "He got the impulse."

"I just felt that she could be a great help in my work," says Singer.

Writing a play one day a week over a three-year period would challenge most writers' powers of concentration. But Singer could write standing on the median strip of an interstate highway.

While in Minneapolis for the opening of "Teibele" last year, he sat down and started writing in a crowded hotel lobby, Friedman recalls. At home, Singer writes while answering phone calls -- on a phone located not on his desk but in the hall outside his office -- at the estimated rate of one every five or six minutes. During calls, he says, he gets ideas for how to proceed with his writing.

After the Nobel Prize, however, the phone calls started coming so fast that "the moment I hung up the phone was instantly ringing." So Singer rented a hotel room for a month and then, "against my will and desire," secured an unlisted number. Now the calls are back to the old rate of one every five or six minutes.

Part of Singer's problem is that he can't say no. "When I go into the shoe store and they don't have shoes that fit me, I buy them because I don't like to disappoint the salesman. I have a whole closet full of such shoes. I cannot let a man serve me and then just say goodbye."

But he has generally resisted exercising one prerogative of literary eminence -- endorsing other writers' works. Tolstoy, he says, once wrote Bernard Shaw a letter of munificent praise while almost simultaneously describing Shaw's plays as "superficial" in his diary. "Writers shouldn't have writer friends," says Singer. "Every piece of kitsch that comes out always has 10 or 15 false witnesses -- brazen lies -- that tell that this is a great masterpiece.

"There were a few times in my life that I have been tempted to praise a person against my judgment," he admits. "But now I have told myself that even if the Almighty should publish a novel, I would not write an endorsement. I would say to Him, 'The creation was all right, but please leave literature alone.'"