Yves Saint Laurent is nervous.

He tugs at his hand-tied burgundy bow tie which he wears with a navy pinstriped fitted suit and pink oxford shirt: like a banker fresh from the barber.

He sits uncomfortably in the velvet armchair, chain smoking Kools wrapping his knees with his arms, finally spilling the water in the oversized crytal glass.

Perhaps it's the missing Proust. In France, he says, he always keeps a volume near, savors the elegant epic of high society, low jealousy and intricate fantasy. But "not in New York," he says. "I have no time."

Which is understandable. He is the most influetial fashion designer in the world, the head of a $150 million-a-year worldwide business including 150 women's ready-to-wear boutiques, $50 million in menswear and three successful perfumes.

Tenight he is launching a fourth. It is already on sale in Europe, where in only 2 1/2 months it has surpassed the sales of the established front-runners like Chanel No. 5.

The fragrance is called Opium, and St. Laurent says he has been working on it for five years. During the same period, he has taken up writing - "It fascinates me, it is my passion" - and keeps a spiral notebook by his bedside, ready to write in when he feels like it. he has written 12 pages about opium.

"In France, opium is related to literature, to poetry at the end of the 19th century, to Rimbaud and Baudelaire.

"It is a mysterious world. You are not obliged to smoke opium to dream. It has the power of evocation. It suggests the Orient, the extreme Orient, all the exotic countries," he says, spinning his own Proustian rhythms.

That is the mood that the increasingly reclusive St. Laurent has authorized for tonight's party to promote the new perfume.

On a four-masted bark - which Charles of the Ritz secured two months ago to decorate - about 800 of the glamourous and the amorous, the chic and the rich, and likely a few clever crashers are gathering amid thousands of cattleya orchids, a half-ton statue of the Buddha and lavish cocktail fare - all illuminated by a Chinese, French and Italian fireworks display discharged from two boats in the East River.

The antique vessel has been repainted and furnished to YSL's standards. He rejected plans for gold lame sails, and designed others of royal purple, gold and black.

St. Laurent has described his new fragrance as "lush, heavy and indolent," and that seems to be the tone for his new ideas in clothing as well.

What women want from clothing now, he says, is seduction and mystery. "For a long time, women lost their mystery," he says. There was an exaggerated looseness to clothes, and women looked like "parachutes."

"They lost control of their movements. They began to be too easy and relaxed. They began to be too easy and relaxed. They didn't even bother with cosmetics."

But all that is changing. "I sense it in the streets. And I want to give fashion not the same clothes in the streets, but the same provocative ideas."

That's why he is designing deep-slit skirts that reveal the leg, or funny circus hats, or gloves in bright colors. "It's provocative," he says.

"Clothes dictate an attitude. Sometimes clothes help a woman find herself, her personality."

"In these clothes," he says, "it is more possible to control the seduction than in parachutes."

When St. Laurent, 42, speaks of these things, his quiet voice and shy manner give way to confidence about his genius, his success.

He says, without smiling, "Yes, I am the best designer in the world. But there are others who do fantastic things," he adds quickly.

"And I am the last real couturier." he says. "I have learned over 20 years from the best, from Dior particularly. I have other marvelous people who help me construct clothes. They are why I continue high fashion. Not for prestige, but because the workmanship is extraordinary and if you cut the metier, you lose these skills."

Reminded that he said precisely that in an interview six years ago, he gives the first relaxed laugh and proclaims "You see, I am faithful to me."

Some of his clothes he feels are completely perfected - citing are example from his last collector, a one-shoulder pink bias-cut dress which he finds both classical and modern.

His classics, such as the safari jackets, the pants, the blousons which he put into fashion first, he says, "are the modern things and they are for the future. They are now as good as they can be."

He thinks that with the next collection, he will have perfected the blazer.

His new design - only 2 sketch so far - is shorter, with shoulders that look broad but are not. "The basic things have been made. Now we can stop," he says.

"The more I advance in work, the more I feel the responsiveness of women and the more the body of the woman dictates the dress and the suit," he says.

"I love woman because she is mysterious. Completely different from men . . . it is difficult to find a mysterious man. I know woman.I understand woman. I love woman in general.

"But I don't care for fashion. I'm a couturier, yes, but I don't think a woman needs a lot of dresses, a lot of jewelry. The woman is first. After that, the clothes."

That will be news to the many women decked out head to toe in Saint Laurent labels at the Opium party last night.