Katharine Hepburn, who almost always wears trousers and almost never accepts an award, showed up -- wearing trousers -- at a festive dinner of fashion designers tonight to accept their top prize, the 1985 Lifetime Achievement Award.

"This is a pretty serious place," said Hepburn, looking out at the crowd seated in the marble-vaulted Astor Hall of the New York Public Library. "Imagine that the original bag lady should get an award for the way she dresses."

Hepburn, who was wearing a black satin coat and trousers and a white silk scarf, told the hushed crowd that "as a child I did resent rather being a girl." At one point she even shaved her head, she said. "But finally one grows up." Her mother was a fighter for women's causes. Hepburn said she herself thought "that skirts so short you showed everything when you sat down was a foolish way for women to dress." She added, "I do have a skirt to wear for funerals."

It was Hepburn's independent style that prompted the award from the Council of Fashion Designers of America (CFDA), said Calvin Klein, who introduced the actress. Klein, who was on crutches from a ski accident, said, "In her 42 films and in her life she has truly epitomized the ultimate American woman. She's vibrant, she's outspoken, she's hard-working and she's independent, and, fortunately for all of us, she's never been afraid to be comfortable. And for that reason fashion designers all over the world have a great deal to be grateful for."

Added Klein, "In 1930 she wore pants and suits considered scandalous; today they are sensational. And they have prompted generations of fashion designers to capture the vitality and the spirit of the woman who has worn them."

There were no surprises in tonight's awards given to Geoffrey Beene, Donna Karan, Liz Claiborne, Robert Lee Morris, plus Ray-Ban Sunglasses, "Miami Vice," the show "Tango Argentina" and the late Rudi Gernreich. Alexander Liberman, creative director of Conde' Nast, was given "the 1985 Lifetime Achievement Award" along with Hepburn. The awards had been announced earlier. The only question was whether Hepburn would show up.

Perry Ellis wrote Hepburn months back asking her to accept this award and when she refused, he wrote again asking if she would accept it without having to make an appearance. "Call me," she wrote back, including her phone number, and for months she was wooed particularly by Calvin Klein and Robert Raymond, the executive director of CFDA. According to Raymond, last Friday she took a walk in Central Park to mull it over.

Saturday Raymond called her when he heard on television she had been in a car accident. "It was just one of those silly four-car pile-ups," she told him. "I'll be there."

In fact, she came to the rehearsal yesterday afternoon to check the setup. When told that the menu included floating island, she told Raymond her favorite dessert was ice cream. So when she arrived at the library and slipped into a chair next to Calvin Klein, the dessert was replaced by ice cream.

This dinner, for which guests contributed $750 as patrons of the CFDA, was underwritten by The Wool Bureau for $150,000. The money is to be used to endow museums that "record and preserve American fashion," according to Raymond.

This was the CFDA's fifth awards dinner. When the group, led by Perry Ellis, decided to present awards to people other than fashion designers, the event became far more interesting. Last year among those getting awards was Diana Vreeland, former Vogue and Harper's Bazaar editor who has guided the extraordinary exhibitions at the Metropolitan Museum of Art, and the Astor Barber, the center for short haircuts for women in New York.

The CFDA awards were given an added boost this year because of the demise of the Coty Awards, once considered the Oscars of the fashion industry. The Coty Awards lost their impact partially because too many awards were given, but also, as designers developed their own liaisons with fragrance and cosmetic companies, they preferred not to give a boost to Coty, the cosmetic company that originated the award.

But clearly it was the award to Hepburn that titillated everyone tonight. Security matched any White House event with the added impolite twist of New York security guards. But for most, including designers who rarely go gaga over anything or anyone, Hepburn was different.

"She is the all-time movie chic," said John Weitz, a founding member of the CFDA. "She's wonderful -- never outrageous and vaguely manly and always her own style," said jewelry designer Paloma Picasso. "She's easy, un-self-conscious and really American," said Jeffrey Banks. "She's the epitome of class -- if there is such a thing as class," said Vartan Gregorian, president of the library.

Hepburn never heard these comments. If she had, she would have been surprised. As she accepted her award, she said, "I am pleased to think I've had any effect at all on anything."

The crowd stood and cheered.