At a fashion gathering at the Whitney Museum last week, a New York designer and a retailer were admiring the Missoni models when a cosmetic executive walked in wearing a black forward-titled cocktail hat made of feathers, with a veil and a silver fox boa.

"My God - what have we done," the two said almost in chorus.

What much of the fashion industry has done is try to make something old work in today's lifestyle. And it just won't do.

Of course, there is no fashion idea than hasn't, in some way, been done before. Skirts and pants have been every length; and silhouettes have been broad or narrow or a combination of the two at various times.

But in the last season or so, as clothes have slimmed down and lost excess layers and details, designers have seen tempted to hitch their styles to eras gone by. There is a certain safety in linking a new line to something familiar so it won't seem so experimental.

After the leisure-suit boom, for example, men's fashions drifted easily back to the tweed sport jacket because it was a virtual classic. Of course the current versions, usually in a softer fabric and far less structured tailoring, are far from simply repetitive of what had been worn before. But the familiarity gave customers a base for taking a gamble.

A lot of people are calling the new clothes "retro," identifying them with the 1940s and 1950s. But the best of the new styles are not retro - they are fresh, spanking clean, pared-down looks aimed at being cool, comfortable and classy when warm weather comes back.

There's nothing wrong with old clothes, they can be quite wonderful. But women's figures have changed in the past 20 or 30 years, and so have their underpinnings. Nowadays, with fewer skilled cutters and tailors, and different fabrics, it just isn't possible or sensible to repeat an old style.

"Sure, I love shoulderpads, but you can't have them too big. You can't go back to the way they were before," says designer John Anthony, whose show on Tuesday featured suits and dresses with light shoulder padding, as well as strapless dresses.

The way to make the latter has changed too, Anthony explains. "The old way was with stiff boning that could stand up by itself on the piano. The current bones are spirally and soft," he says as he takes the top of one of his strapless dresses, rolls it in a ball, and throws it on a chair. 'The new ones you can roll up and stick in a suitcase.'

What is modern, Anthony, says is doing things in the simplest and sexiest way. Like his suits with only a simple see-through nubby silk tank-top underneath. "I hate accessories. Why make women look like Christmas trees? I like the simplest hair and good makeup. You can't give me hats, veils, gloves and the rest of it."

But he and others have revived the lace dress. "I used to hate lace. But then I found a beautiful young lace," says Anthony, discussing lace flowers carefully scattered on satin. "When you show it with no underpinnings, and it is very see-through that is the youngest lace of all," he says.

Geoffrey Beene kept using the word "clarity" as he talked about his new collection, which many consider his best ever, in his office the day before the Wednesday showing at Lincoln Center.

"Our society must face a lot of things in the 1980s, economic and social problems, and therefore we need more clarity in clothing. Things have to be simpler to put together, to make life easier," says Benne, who claims his business is up 182 percent over a year ago. ("I didn't know that there was a figure over 100 percent," he says, laughing shyly.)

"If wealthy women don't have the time to put all the parts together, how can we expect others to deal with too many options?" Beene asks.

If Beene has pared away most of the innumerable options in dress, he hasn't overlooked versatility. "That's why I prefer suits to dresses." His very freshest design, an iridescent chiffon evening suit, can be worn belted or not. And the top is so light that it can be worn tucked in like a blouse.

Any excessive designing, anything too tight or too sexy, is not modern, he says. He's against the very "tart-y" look of some clothes today with short, slit skirts, clingy fit, skinny pants and stiletto heels. "Why put women down at the moment when they are doing so much?" he asks.

Koko Hashim of Neiman-Marcus agrees. She's all for the "femaleness" of the new clothes, but with quality and taste. "We're moving away from having to hide behind a man's blazer, a man's shirt and men's trousers to wear to work," she says. "Women have reached a level of confidence where they can move in the professional world as women, not pretend men."

But whether that impulse will carry into retro clothes remains to be seen. One Washington husband caught a glimpse of his wife all dolled up in a hat and veil and black gloves to the elbow, and exclaimed in all sincereity, "My dear, you never told me we were supposed to go in costume."