Rudi Gernreich, avant-garde fashion designer who paved the way to the 1970s with knits, nudity, molded clothes and what is now a totally accepted concept of comfort in clothing, was back at the Smithsonian Tuesday night ot give a multimedia presentation on the past, current and future state of fashion.

These days, Gernreich is busy designing costumes for the very mordern California-based Lewitzky Dance Company. His totally stretch dance costumes are so closely programmed into the choreography and decor that it is somethmes hard to tell where one thing begins and the next one starts. For example, his "duotards" -- one garment for two people -- limit the dancers and affect the way they perform.

And he is currently negotiating contracts for a new collection of dance clothes and furniture.

Gernreich dropped out of the fashion business in the late 1960s when nostalgia replaced the contemporary clothes he had pioneered. What went wrong?"We were looking for a staggering thing when we went to the moon," he explains. "We were expecting a whole new source of something. But then we discovered a dead, completely dead planet. And in our disappointment, we went back to the old, the romantic."

Backstage at the Carmichael auditorium, Gernreich snapped open his shiny aluminum suitcase and took out the two zipper-pocketed jumpsuits in black velvet and gray flannel he might choose to wear for his lecture, replacing the cotton flight suit he had worn on the plane. And he painfully turned away a couple of models who weren't suitable to wear his bathing suits and disco clothes on stage. "You really are very nice," he said, kissing them on the cheek as they left.

Among the things he told the 200 people attending the lecture series on costume were:

Clothes are costumes. What you can say and what you do say with clothes is very important . . . In periods in which clothes take a very conservative attitude, that is symbolic of what you are not saying, and in a sense this is costume also.

"After the topless suit the bikini became a staple. The bikini had been the most daring attire, but once the topless was there, the bikini became a watered-down maillot.

"In the late 1960s, if you walked down the street and everyone looked at you, focused on you, that was very good, very positive. The '70s are more sober, more subdued. We are living in a difficult time. People are afraid We live in modern (apartment) fortresses. Until recently, people wanted clothes that were anonymous.

"I did the military look in the late 1960s because some designers were making Scarlett O'Hara clothes, which I thought was an insult to women when they were becoming totally equal to men.

"What I would change in my projections of ten years ago is the attitude of the woman. As I look at what I did, the feamle figure is subservient to the male. It is disturbing to me to see that.

Knits are a terrific medium for mass production. There is no one who is a perfect size. Knit fabric adjusts to the body . . . The great new fiber is Lycra, which for the first time stretches both ways equally.

At a certain time in one's life, when the body is no longer very attractive to look at, it should be abstracted. You would wear a big robe-like garment with hold patterns to detract from the anatomy of the body that is no longer young and beautiful. The fact and head should become the focal point and express some experienced life.

Clothes don't always have to make a statement -- and when they do, aren't they a bore?"