According to fashion designers who wound up their showings for fall here last week, it is a sophisticated, confident, sometimes even agressive kind of woman who will be dressed in their clothes next season.

Skirts that swing open with a long stride, flashy, funny fur pieces over broad-shouldered and belted suits and blouses that plunge to the waist add up to sexiness, but it's more glamor a-la-Greta Garbo than the some-like-it-hot variety.

The rest of the look, as fashion gurus see it, is rounded out by stilletto heels, long hair and red lipstick, dark colors (particularly black) and natural fabrics, including feather.

So is any nice female government lawyer going to keep a date in court next fall looking like a modern Barbara Stanwyck?

As always, the extremes of some New York designers will be much diluted and modified by the time their concoctions arrive on the sales floors of Washington stores and boutiques. A certain fraction of what comes down the runway in Paris, Milan or New York is done for amusement and attention-getting anyway. And existing popular styles, including the Annie-Hall look, are likely to go on and on.

But what buyers, reporters and an ever-bigger gaggel of celebrities like Bianca Jagger, Andy Warhol, Ali McGraw, Bob Evans and Annie Hall herself, Diane Keaton, saw last week is a definite shift toward grown-up, confident sophistication for daytime as well as night.

There are sexy evening clothes that almost fall off the body or scarcely veil the wearer, and a look meant to be worn to the office that in many cases uses shoulder pads for a broad, roomy look at the top, more slimness toward the bottom. Belts, which add to the shape, high heels and big fur pieces carry out the effect.

All of which is based loosely on a perception that women are ready to look more and more womanly, to please themselves, perhaps, rather than to attract attention from men, as in the past. A Paris designer, Claude Montana, sees this as a new female aggressiveness, but another Parisian, Karl Lagerfeld, says simply, "It is a new kind of confidence and sophistication about sexuality."

"I'm tired of the casual (young, little-girl look," says Bill Kaiserman, the designer for Rafael. "There is nothing more fantastic than a young person looking sophisticated."

So while his clothes are still soft and even drapey on top always with substantial shoulder padding, his skirts usually are slit open to the hip. But with buttons to close them as much as the customer wants.

Calvin Klein, who has been using shoulder pads in jackets and coats for three years, has shown jackets for day worn over wrap blouses virtually opening to the waist. But now Klein admits "they are not for every office" and has told women to anchor them shut with a pin if necessary. For fall, Klein not only showed them pinned, but often added a filler of cashmere - a ribbed or lace sweater - underneath to make the outfit not only more proper but warmer, too.

Halston, long a master of simple, sexy clothes, also made his daytime clothes more glamorous with dyed-to-match fur pieces (complete with heads and tails) to go with his suits, pants and skirts.

To make sure women can walk easily in his narrow skirts, Halston has gone back to cutting skirts off just below the knee.Klein, on the other hand, finds the proportion more contemporary with hemlines cut just below the calf for day, longer for evening.

Stephen Burrows, in his show at Bendel's on 57th Street, made a pitch for the short dress for discos. Short or long, Burrows likes movement in all the clothes with fringes and feathers flying in all directions. "It is the way we wish women would dress for Studio 54," said Bendel's president Geraldine Stutz after the showing. Groned one buyer, "The only problem is that people who go to discos can't afford designer clothes."

But price appears not to be a concern of designers in this league. Geoffrey Beene has a cashmere blazer that is expected to retail as part of a costume for $3,000.

Designer Mary McFadden, a favorite with Washington women for her evening clothes in spite of their $1,000-and-up price tags, has now added daytime styles. Her inventiveness carries over to fluffy mohair sweaters, handpainted suede and extraordinary textured wools.