When the invitation says black tie, men know precisely what to do. Occasionally, they get cute -- red bow ties at Christmas, cupid suspenders on Valentine's Day -- but genuine stiffs will have Cary Grant on their minds when they put on their penguin suits. Women, on the other hand, are not so predictable.

These days everyone has her own idea of formality. At the Kennedy Center Honors last week, it was possible to see Katharine Hepburn in Reeboks and Georgette Mosbacher in Dior. Both were appropriately dressed, given their different objectives, though neither would have looked right if Mosbacher had on the sneakers and Hepburn the strapless gown. Formality is as much a matter of personality as of place. Wearing tailored trousers to the White House, Glenn Close wasn't underdressed so much as overcast: Just how many Hepburn characters was she playing that night? And yet her homage outfit was also a respite from the bloated chic that often passes for elegance.

Alas, there is no consensus on the black-tie issue. If people think Washington is too conservative for such concoctions, it is at least democratically adjusted to seeing minis and ball gowns in the same room. Even so, the legitimate wearer of evening hot pants -- so popular in New York -- would likely get a cold shoulder in Washington and almost certainly a table behind a potted fern. At Saks Fifth Avenue in Chevy Chase, where the charity set gathered last week for a fashion show by Carolyne Roehm, the operative mode was the little black dress or cocktail suit. Up on the runway, though, the designer was proposing a very different look: skimpy slip dresses and bouncy eyelet frocks. A group of men standing in the back row looked puzzled.

"Where would you wear dresses like that?" asked one. "I can't see them at any of the benefits I go to."

So what does he know? The only challenge men face is the holiday invitation that calls for "creative black tie." No doubt the host of such a party has carefully selected his guests, eliminating anyone who works on Capitol Hill, shops at Brooks Brothers or drives a Volvo wagon. In other words, practically every male in Washington. For those who are still confused about the "creative" stuff -- reindeer cummerbunds, elf hats and the like -- consider the advice of the late fashion writer John Duka: "White tie is worn only with tails. Tails are worn at only the most formal occasions, inaugurations for example. Red ties are for band leaders. And short dinner jackets are for those who work in restaurants."