CORNELIA GUEST comes in from the wind blowing at 59th Street and Park Avenue to Cafe Reginette, the Manhattan restaurant frequented by South American playboys, English disco dancers and hipsters from Queens. She wears black leather pants and a coyote fur coat. She has blond, glamor-girl hair, a silky complexion and a pretty, red mouth that forms a small pout. In 1982, the New York press dubbed her the "Deb of the Year."

She is the goddaughter of the Duke of Windsor, and often dances at Studio 54 until 4 a.m. Among her friends are Francesco Scavullo, the photographer, and Mick Jagger, the rock star. She says she went to 500 parties last year, although she later amends that to 365. She wants to be an actress.

"Bonjour," she says to Sylvain Snanou, the Reginette manager. They kiss. She's just back in the city from Palm Beach and Aspen, where she says nothing happened at night. She walks over to the table, pulls out a package of Marlboro Lights, then orders champagne. It is 3:30 in the afternoon. She is 19 years old.

"I had a wonderful year," she says. "I had some bad times, but you know, God, it was just a year where I met more people. There were so many great things." She has dramatically madeup eyes, and a soft, luscious fullness to her face and upper arms. "And I loved the parties and . . . "

The manager interrupts.

"Oui?" says Guest.

"Mr. Persky's on his way," he says. Producer Lester Persky ("Hair"), fiftyish, is one of her best friends. He arranged the interview.

"Ah, merci beaucoup, great, thank you," says Guest.

"It was a wonderful, wonderful year," she continues. "It was, you know, one of the best. God, I'm young, but it was probably the best year of my life in certain ways. And the worst. Because my father died, I mean, you know. The two together."

Her father was Winston Guest, a second cousin of Winston Churchill, a descendant of the first Duke of Marlborough and an heir to the Phipps steel fortune. He once was ranked one of the top 10 polo players in the world. Her mother is the very social C.Z. Guest, of New York, Long Island and Palm Beach. She writes a gardening column and has been to the White House as a friend of the first lady.

Tonight her daughter will sing "It's My Party and I'll Cry If I Want To" on the David Letterman show. On New Year's Eve she sang at Xenon. She came out at the Debutante Cotillion and Christmas Ball at the Waldorf-Astoria. At 15, she dropped out of Foxcroft, the Virginia boarding school, to ride horses. She got her degree by mail. She thinks the Equal Rights Amendment is "pompous" and "ridiculous." Her ambition is to win an Oscar. She has a 42-year-old boyfriend, Peruvian real estate developer Roberto Riva. Not too long ago, she forgot and called him "Antonio." Despite her good fortune in life, she says she does get depressed. "Sometimes my dog will get run over," she says, "or my horses get sick."

Debutantes have been back in style for several years, but no one since Brenda Frazier has made such a splash as Guest. Frazier, the 1938 "Deb of the Year" who appeared on the cover of Life, died in May after a nervous breakdown--and publication of a 1963 memoir called "My Debut--A Horror." "It's a tragedy that she died," says Guest. "She was a wonderful woman. So beautiful." Guest's mother had her own celebrated debut the year before Frazier, right at the end of the Depression. Her daughter, who has been told of the current recession, thinks there's a reason that money is flaunted in bad times. "It's partly because people feel so bad about the economy," she says. "They want to get dressed up and feel good."

The door of Cafe Reginette opens. Persky. His hair is mussed and his coat is hanging from his shoulders slightly askew.

"Pesky, darling!" says Guest, lighting up. "You look like something the cats dragged in. What's happened to you, my darling? You've lost so much weight."

They kiss.

"Forgive my cold hand," says Persky. "I walked up Third."

"It's good to be home," says Guest. "God, you miss the city. Pesky darling."

"Pesky," says Persky, slightly annoyed.

He orders a Virgin Mary and pea soup, then addresses the question of how and why Cornelia was chosen "Deb of the Year."

"Well, the first I knew that the press was showing any particular attention was when we went to the opening of 'Ragtime,' " he says. "Suddenly the bulbs kept blasting, and I knew it wasn't just me, because I didn't do the movie. This was a year and a half ago. The next day someone gave me a copy of Women's Wear Daily, and here, dominating the whole spread--which included the director, the stars, Mayor Koch--was this huge picture of Cornelia with me next to her, saying, 'The Deb of the Year.' Suddenly, she was the Raquel Welch of the year. Of course, I think it's just that Cornelia is one of the few people who has the credentials. And she looked like her background. Very pretty, blond, young, a little plump then. She's better now."

"Lester!" says Guest.

"And she had clothes," Persky continues, "and she knew how to wear them. She was a storybook princess, an old-fashioned American princess. And here she was, with an unlikely person, me. They were ready to pounce on her. And of course, Cornelia had all the things they wanted. She really was the first gal, I think, since--what were they called, the hippies? The public was ready for a new mood, a groomed mood. No beads."

Does she agree with all this?

"I don't agree that I was plump, at all," says Guest.

"You weren't very plump," says Persky. "Just a little baby fat."

Does she like being described as pretty and sweet, or would she prefer elegant and sophisticated?

"Yeah, Lester," says Guest. "Puppy dogs are cute and sweet. But I'm still happy. It's better than nothing, Uncle Lester. Right?"

"I would say that Cornelia is, outside of pulling a few bank jobs or getting kidnaped, I mean, it's the only way to really get your name in the paper," says Persky. "You're quite right to be pretty and sweet."

"I think so, too," says Guest.

(Her mother, interviewed later by phone, has another explanation for her daughter's sudden fame. "I was thinking about it while I was riding," she says from Palm Beach. "First of all, her mother and father were famous people. I've been on the cover of Time. I was named best-dressed woman in the world. I have a gardening column and I have millions of readers. I have thousands of orchids and several greenhouses. She's a very beautiful girl. I understand why they chose her.")

Back at Cafe Reginette, her daughter is asked if she ever feels guilty for being rich.

"She's very kind to horses," Persky replies.

"I love my horses," says Guest. "Lester came to the horse show this summer out in Southampton. And at a horse show you wait for hours, let's face it. And it was all muddy. And he's standing there with his sneakers on. Remember the mud?"

"My house was in the same town, so it was worth it," says Persky.

"And his Rolls Royce got stuck up to the hub caps on our way to lunch," says Guest. "We had so much fun."

Does she ever think of using her position for the social good? Caroline Kennedy, who is just a little older than Guest, once spent a summer in Appalachia.

"Appalachia?" says Cornelia, wrinkling her nose.

For two years, this Deb of the Year was living on the East Side of Manhattan with a roommate. "It's an absolute mess," she told New York magazine last year. "I've got to do something about picking fabrics." But the new year finds her back at home with her mother on Park Avenue. What happened?

"We don't discuss that," she says.

"She's back in the family nest," says Persky. "They really have a very comfortable apartment on Park Avenue. High 50s. Almost the low 60s. It's very nice. Very good doorman."

"Oh, we have the best doorman in the world," says Guest. "I love the apartment. It's just . . . "

"She wasn't a good housekeep. . .," says Persky. His voice drifts off.

"No, I was fine," says Guest.

"Roommates, roommates," says Persky.

"I don't want to talk about it," says Guest. "It makes me sick."

"Is that what she said, that it makes her sick?" says her ex-roommate, a 23-year-old Sarah Lawrence graduate named Lisa Burgis. She is talking later, by phone. "Oh God, I don't know what to say. It's a long story."

She makes it short: "I threw her out because of competition over a boyfriend." There is no elaboration.

"I have no comment," says Guest about Burgis' claim, "because she's nothing. She's no friend of mine. There's no point in giving a girl like that the time of day."

"Cornelia, when she was living with me," says Burgis, "was always depending on me to take care of her. We were both really social, but she was just a bit . . . ridiculous."

C.Z. Guest thinks not. Her daughter "had a very structured family life" and therefore "has a discipline over herself."

("I had a governess for my children," she said in a 1977 Washington Post interview. "I think children are better brought up with a governess. Children need someone to discipline them. And after all, Winston didn't marry me to be a maid. Besides, I couldn't go around with Winston, traveling, doing all the things he wanted me to do, if I'd had to stay home and take care of the children. That doesn't mean I never saw them. Of course I saw them. I went fox hunting with them.")

Now, says C.Z. Guest of her daughter, "I don't tell her what to do. If she wants to stay out late, it's her choice. She's 19. She can vote."

Although she might have some trouble with that. Back at Cafe Reginette, when asked if she is a Democrat or Republican, Guest turns to Persky for an answer.

"Don't look at me," he says.

Guest is working her way through the pack of Marlboros. "I hated school, and I hated being away from Mom," she says about Foxcroft. "It just wasn't the place for me. I just like to be with my horses and my dogs and my parents. And I was very into my riding. The level that I rode at just wasn't available at Foxcroft. And I was away every weekend, and my trainer would come in, and it's hard when you're in a different surrounding. At a boarding school, they have certain rules. You can't have your own coach come in. I just couldn't really go on and fulfill myself as a rider as much as I wanted to. So I left."

Her mother not only supports her decision, but takes responsibility for it. She says the headmaster first told her that her daughter could leave school for six weeks on the riding circuit, but then said she couldn't. "I was really furious," says C.Z. Guest. "So I just sent the van to pick up her horse, and our man. I sent for her clothes later."

These days, Guest's clothes are by Fabrice, her favorite designer. He frequently loans them to her for big events. "Sometimes she buys them, sometimes I give them to her and sometimes she just wears them for a night," he says. His birthday gift to her was a silk taffeta, short evening dress that retails for $1,400. Asked what Guest has purchased from him, Fabrice says: "Ummmm. God. It's been so long. Ah, a beaded tunic dress and a black dinner dress. I do a special price for her. It's usually a little less than wholesale"--or about 60 percent of retail. "She's very good for my clothes," he adds. "It's very good publicity for me."

On this night, Guest is just planning a casual dinner with friends, and then a trip to Xenon. She hasn't been out in a week.

"I've spoken to everyone on the phone," she says. "And I'm just like, 'Hi, how are you?' and they say, 'God, we haven't seen you. What do you look like?' You know."

"They'll be suprised," says Persky.

"They will be suprised, won't they Lester?" says Guest. "I think it'll be fun to go see some pals again and do it once a week. Once every few weeks. Everything is going to stay exactly the same in New York. Nothing is going to change, the people aren't going to change, the parties aren't going to change. So what's the point in going out every night?"

"Go out once a month to see what happened," says Persky.

Does she think she'll be able to stick to that?

"Yeah," says Guest. "Well, no, no, no. Wait a second. There are different charities that I work for. The National Council on Alcoholism and the New York affiliate."

"That's a good one," says Persky.

"That one I'm very, very strong with," says Guest. "And what's the other one? Ummmmmmm." She seems puzzled.

Persky tries to be helpful. "Aren't you following the Jockey . . . ?"

"Yeah, the Jockey Club foundation," says Guest. It's a foundation for retired and hurt jockeys. "And the April in Paris Ball. Which is 15, 16 charities. Oh God, I've been out of this for so long."

Last fall, Guest told People magazine she was "interested in some of the diseases." Which ones?

"There are charities that I believe in that I will work very, very hard for," says Guest. "But it's not like, 'some of the diseases.' I mean, that sounds really, you know."

"Most good diseases have been taken over by some ambitious ladies," says Persky. "It's hard to break in to the really big diseases."

A waitress comes to the table. "Sorry to bother you," she says to Persky. "But did you order a cheese omelet?"

"No," says Persky. "Perhaps yesterday."

The debutante is asked what women she admires.

"I admire Nancy Reagan," she says. "I think what she's done to this country is marvelous. I admire . . . " She pauses. "Love Bette Davis. I think she was a wonderful actress."

"Is," says Persky.

"Is, is, is," says Guest. "Excuse me. Is. I admire my mother. I think she's wonderful. I admire . . . " She pauses.

"So you don't admire people just for the way they look?" says Persky.

"No," says Guest. "Some of them, yeah. Well, no, how hard is it? You know, I don't think it's very hard to go out and buy a new dress every day. You take a credit card to Bergdorf's and you go and say, 'I want that.' And you put it on, and if it looks okay, you take it."

Is that what she does?

"Nooooo," says Guest, her mouth in a pout. "I don't do that. I really don't."

"She promotes dresses for these designers," says Persky. "She's always showing up with a new dress."

"I really don't go shopping all day," says Guest.

"She doesn't spend a lot of money," says Persky.

"I don't," says Guest. "I don't shop all day. Fabrice is my favorite designer, okay? When I have to go to a big thing, I usually wear his clothes."

"How about that dress he made for your birthday party?" says Persky. "That wonderful dress."

"That was Fabrice," says Guest.

"It was a knockout dress," says Guest. "It was the most beautiful dress. It was strapless." She pauses, savoring. "It was black."

"Before black was big," says Persky.

"And it had a black little bustier," says Guest, "and then, in the back, it was like, tulle, dark tulle then lighter, and then dark and then lighter. With petticoats. It was the most beautiful dress. And then Way Bandy did my face. Gerard Bollei did my hair. And it was a knockout dress."

But what was done to her face?

"Way?" says Guest. "He just . . . "

"Washed it," says Persky. "Heh, heh, heh. That's all you needed. You were only 18 then."

"Lester, you are terrible!" says Guest, annoyed. "You should wash your face. You look like you have enough dirt on your face. Have you been rolling in the mud?"

"Dear, dear, you see, you didn't even understand what I said."

"I do . . . "

"When you say about someone that all you need is to wash the face and let it alone . . . you don't need stage makeup."

"I don't need anything."

"She really did look great," says Perksy. "It was a wonderful dinner party."

But what was done to her face?

"God, no one can do it like Way Bandy," says Guest. "He's the best. He put false, no he didn't put false eyelashes on me. He just made me look incredible. Because he knows my face very well. He knows just what to do with it."

And don't forget Fabrice: ""Fabrice knows me so well, Fabrice knows my size, he knows just everything, he knows what I like, and he's such a wonderful person," she says. "We can always figure out something very quickly, or plan it."

She can call him and say,"I'd like something like this"?

"Well, yeah, if I'm in a big mess," says Guest.

"Valentino," says Persky.

"And I also love Carolina Herrera," says Guest. "She does beautiful clothes." She pauses, sighing. "That Valentino party. It was a beautiful party. My mother and I wore the same dress." She starts to laugh. "My mother went earlier. My dress hadn't come yet. I was getting my dress from Carolina. And my dress came, and then we got there, and there was my mother, and I thought I was seeing a mirror image of me. Oh, Mummy."

"It was terrific," says Persky.

"It was great," says Guest. "We looked like two little twins. We were sitting on the same chair."

But how did her mother happen to have the same dress?

"Don't ask me," says Guest.

It is dark outside, and getting close to the cocktail hour, but Guest and Persky are busy reviewing the year.

"I would say that Cornelia went to maybe 300 parties, of which 250 you could never recall, or 275," says Persky. "There are maybe five that would come to mind now."

"There was Valentino's," says Guest. "My birthday at Xenon, on December third. Then the National Council on Alcoholism, where I sang. The Christmas party, where I sang--at Xenon last year. Then Lester's 'Save the Trees,' where we showed up without a tree. This was in Studio 54. Um, where else?"

What trees were they saving?

"That was Save the Children, not Save the Trees," says Persky.