ora Ephron slathers tuna salad onto a half slice of Pepperidge Farm cracked-wheat bread. The salad is creamy, with large chunks of tuna and small slices of celery. It was missing the celery until she sent out for some from the store. It's just not right without the celery, Ephron insists.

There's also a bowl of egg salad next to a small glass dish that looks like an ashtray. It's a receptacle for dead tea bags.

"Jasmine or Lipton?" she asks, going to the cupboard.

Her Manhattan kitchen is sunny and spacious, with flecked Laura Ashley wallpaper and an aquarium gurgling in the background. She pours the tea, settles into a cane-bottomed chair and talks about "Heartburn," her new novel.

The book is a slim, thinly disguised account of the last two months of Ephron's marriage to journalist Carl Bernstein, former Washington Post investigative reporter and coauthor of "All the President's Men" and "The Final Days." It describes how "fairly short" Washington columnist Mark Feldman (Bernstein) falls in love with "fairly tall" diplomat's wife and hostess Thelma Rice (Margaret Jay, wife of former British ambassador Peter Jay) while his small-breasted cookbook author/wife Rachel Samstat (Ephron) is pregnant with their second child, cooking so much she doesn't notice her marriage sinking like a souffle'. It talks about their sex life. It talks about their friends' sex lives. It talks about Rachel's cooking and intersperses her recipes for a dozen or so dishes, including borsch, bread pudding and cheesecake. Mostly it talks about how Nora Ephron felt watching her celebrity marriage collapse.

Devastated. Betrayed. Humiliated.

"That moment when you not only realize you've been betrayed, but that an entire part of your past has been robbed of you," she says, trying to explain the heartburn. "You've probably never been betrayed, have you?"

Not one to lick her wounds in private, Ephron--acerbic author of three highly successful collections of essays, "Wallflower at the Orgy," "Crazy Salad" and "Scribble Scribble"--went public with her pain, leaving friends, readers and reviewers to argue over whether "Heartburn" is a "Hubby Dearest" or a wry, honest account of a "perfect couple" uncoupling.

"Everybody is not going to like this book," Ephron says.

She is 41, a thin, intense woman, with dark hair swept off her face and a distinctive nasal voice tinged with a mild New York accent. She wears a cream-colored silk blouse, cotton sweater vest and jeans tucked into brown leather riding boots. A diamond bangle bracelet circles her left wrist. Her brown eyes are deep-set, and her left eyelid has a tendency to droop a bit, giving the impression that she's scrutinizing you. Taking it all in.

To understand Nora Ephron, it helps to know that she is the eldest daughter of Henry and Phoebe Ephron, Hollywood screenwriters whose credits include "Desk Set," "Carousel," "Daddy Long Legs," "There's No Business Like Show Business" and the hit play "Take Her, She's Mine," based on Nora Ephron's letters home from Wellesley College. Everything was copy to the Ephrons.

Which explains why Nora Ephron wrote "Heartburn."

"I've always written about my life," she says. "That's how I grew up. 'Take notes. Everything is copy.' All that stuff my mother said to us. I think that it would have been impossible for me to go through the end of my marriage and not written about it, because although it was the most awful thing I've ever been through . . . it was by far the most interesting."

She takes another bite of her tuna sandwich.

"I don't think it was a catharsis as much as it was a way of taking the basic experience and trying to make it into something else."

That something else, she says, is comedy.

"If you can turn a disaster into a funny story, then it's not as if the disaster happened to you, it's as if you happened to it. You don't control it, but you have the illusion of control. It's at least your version and if you tell it well enough simply by seeing some humor in it, you are not quite the victim of it that you have appeared to be. I grew up understanding this as clearly as any child could have understood anything."

Is writing about it, then, a way of getting over it? She smiles. "Sometimes when you write things down you have the illusion you've gotten over it. But all you've really done is write it down."

And writing it all down can be dangerous. As Ephron observes, "The truth not only sets you free, but sometimes makes life more complicated."

Mildrid Newman, coauthor of "How to Be Your Own Best Friend" and Ephron's real-life therapist, was the model for the therapist in "Heartburn." Newman is reportedly upset over the book.

"I don't really want to talk about it," Ephron says. "But it is certainly true that she was not happy with it."

Margaret Jay, now separated from Peter Jay, said from London that she had not read the book. Asked about reports that she was ready to write her own version of the events, Jay said, "I would not do that." She is aware of Ephron's unkind portrayal of Thelma Rice, a woman with "a neck as long as an arm and a nose as long as a thumb and you should see her legs, never mind her feet, which are sort of splayed." Jay laughs. "She does write very ingeniously and amusingly." As for her current relationship with Bernstein, Jay will only say, "I live in this country and he lives in America."

Bernstein, whose reputation as a ladies' man was well known before his marriage, is reduced to the fictional Mark Feldman, "a piece of work in the sack" who is nevertheless "capable of having sex with a Venetian blind." Bernstein, now a television correspondent for ABC News, says, "Obviously, I wish Nora hadn't written the book. But I've always known she writes about her life. Nora goes to the supermarket and she uses it for material."

Is Ephron worried that men will shy away from her in the future?

"I don't know. The person I'm with now doesn't seem too worried about it." (That person is New York magazine contributing editor Nicholas Pileggi. She had also been socializing with Mort Zuckerman, real estate mogul and chairman and principal owner of The Atlantic magazine.)

Does she feel queasy at all? Opening her sock drawer for everyone to rummage through?

"I don't really much want to talk about it," she says. "I don't want to seem to be defending it. I just couldn't imagine writing a book about a marriage where you didn't say something about sex. That's a question in the reader's mind. I think I was being extremely . . ."

Generous?

"I barely did write about it," she says, hinting that her reportorial pen, usually dipped in vinegar, was watered down this time.

Besides, she says, "my sock drawer got opened when my marriage ended." At the time, she says, the public appetite for private details of the Bernstein/Ephron split trailed her "like a kid's blanket." Which is another reason she wrote the book. To satisfy some of the craving. "But the truth is the sock drawer is only open about an inch. People may think they know about me, but it's really very similar to my essays. If you can do it at all, you give people the illusion of knowing you when all they really know is what you mean for them to know."

And what Nora Ephron means for us to know is her version.

"I didn't feel 'Heartburn' was controversial. I did think that it was funny. And I thought it was probably going to sell. Even now that it has kicked up its little tiny, tiny dust storm of controversy, I don't think it has much to do with the book. When people talk of revenge, they can't have read the book because it isn't a vengeful book."

The first printing was 40,000 copies, and it has already been selected as a featured alternate by The Literary Guild and excerpted in the premiere issue of Vanity Fair.

Nora Ephron's choice of a second husband (her first marriage to author Dan "How to Be a Jewish Mother" Greenburg ended in divorce in 1973) may turn out to be a financial blessing. Mike Nichols, who directed Ephron's screenplay of "Silkwood" (based on the life of Karen Silkwood, starring Meryl Streep, which will be released this fall), is reportedly ready to buy "Heartburn." "It's not firm. It's not set," Ephron says.

Will she make tons of money?

"I'll make a little money. I certainly hope so."

She and a friend, Alice Arlen, who collaborated on the "Silkwood" script, are currently working on a project for Diane Keaton, "Modern Bride," and after that, Ephron says, she will do a remake of "The Lady Eve."

Which is ironic, given Ephron's introduction to Hollywood. Born in New York, she accompanied her parents to the West Coast around 1945. "I knew the second we were there that my life had gone to hell and that if I could just get back to New York, everything would be all right."

She grew up in Beverly Hills, attended public schools, played volleyball and eventually decided to become a journalist. Her first published pieces appeared in The Los Angeles Times. She phoned in the girls' basketball scores, but the paper wouldn't print a girl's byline, she says, so they used "N. Ephron," or "Norm Ephron."

She laughs. "Those were the days."

After college, she returned to New York, working as a researcher at Newsweek before landing a job at the New York Post. She stayed for five years before launching a successful free-lance career and eventually winding up as media columnist for Esquire magazine and an occasional contributor to The Washington Post. Her writing, particularly on women's issues, was pithy and intensely personal, touching on her small breasts ("A Few Words About Breasts"), sex fantasies and her looks ("On Never Having Been a Prom Queen").

"I don't think I'm a great writer," she says. "I think that I have a voice and that that is not nothing. I think I have a way of writing that, whatever it is, is very clearly me writing it."

And her success has nothing to do with luck, she says. "I work very hard. I'm much more hard-working than I am talented. I don't feel I was particularly lucky. I do feel that I was very driven."

She says she felt "like a fish out of water" when she married Bernstein and moved to Washington in 1976. The disadvantages were numerous, she writes in "Heartburn," not the least of which was the lack of a decent bagel. On the other hand, there is one advantage to living in Washington. "There's so little to do there, you can get a lot of work done. I was very productive."

She and Bernstein shared an apartment in Washington and one in New York. When the marriage ended in December 1979, she returned to New York with her two sons.

She began writing screenplays to support herself, then found herself drifting off to the story of her marital fiasco. Was it kosher to go public?

"All novelists write about their marriages," she says. "It's just that most of their marriages haven't broken up in People magazine. I'm not putting myself in John Updike's class, but all the 'Maple' stories are about his first marriage. While the marriage was still going on it was breaking up in The New Yorker magazine! I think what's interesting is people get so puritanical and odd about it when, whose life are you going to write about?"

Not to put herself in the same literary league, she insists, but "Saul Bellow wrote about his marriage breaking up. Bruce Jay Friedman wrote about his marriage breaking up." She taps her fingers on the table top. "Divorce is essentially the major subject of American novelists."

The doorbell rings. It's a messenger with a large bouquet of helium balloons, sent by a friend to celebrate Ephron's appearance on the "Today" show that morning.

She moves to the living room of the apartment, decorated in pastels, scrubbed pine and antique quilts. Her 3-year-old son, Max, who was born premature as her marriage to Bernstein fell apart, is home from school, playing on the Plexiglas coffee table.

Nora Ephron says she has no insecurities, and is "known for being funnier than I am. I'm not as quick as I have a reputation for."

She rubs her eyes. The left eyelid is drooping with fatigue. She doesn't want the photographer to shoot her straight on. She doesn't want to sound defensive. "Please," she says, "don't make me sound too defensive."

She is asked to address the question of living one's life as an open book.

"I'm not writing to be obscure, and no one is. It would be terrible if what I wrote fell by the wayside. If the price you pay for its not falling by the wayside is you lose a certain amount of your privacy, I'm not going to be one of those people who complain about it. It's like women who complain about being beautiful," she says, a small smile crossing her face. "I mean, who are we kidding?" NORA EPHRON'S TUNA SALAD

7-oz. can Bumble Bee solid white tuna

Hellmann's mayonnaise

2 stalks celery, chopped

Drain tuna. Put in bowl with as much mayonnaise as you want. It has to be Hellmann's. Add celery. Put on bread. Eat.