They wore storm-trooper coats, leather Nazi caps, black leather blousons, chains and leather bras in some of the early fashion shows of french ready-to-wear for fall this week.

"I'm only disappointed they forgot their whips," quipped Roy Witlin, head of Nan Duskin, a Philadelphia specialty store, as he left the France Andrevie showing yesterday. France Andrevie is a hot and trendy house these days.

Murray Friedman of Bloomingdale's reacted similarly. "It's all too reminiscent of a time we would rather forget."

These spinoffs from the subcultures of punk, leather homosexuality, neonazism and the blouson noirs (the motorcyclists in Marlon Brando grab) are being endorsed by minor-and major league designers here in their early shows for fall '78, including Tattarachi and even Yves Saint Laurent in some of the styles in his fur collection shown yesterday.

But these aggressive styles apparently aren't at all for American tastes, though many young French girls here already have adopted them, and they are thought to be an indication of a big leather season.

Paris is Round Two in next fall's European fashions. Round One ended last week in Milan, where Italian designers showed many designs featuring the military look perhaps stemming from the nation's current problems with terrorism, padded shoulders and lots of leather. Dozens more Paris shows are scheduled for the upcoming week.

Fashion buyers have arrived here at a very "up" moment following a period of several months before the recent national election when the feeling for many was one of gloom. That pre-election feeling is expected to show up on the fashion house runways in somber-colored, man-tailored clothes already hinted at in many of the houses.

But for Karl Lagerfeld, who sports a George Washington hair style and a black chiffon scarf tied in a bow at his neck, the past period has made him want to do more adventurous styles.

He has invented a new fake fur using carpet-making looms and, proposed a one-legged dress (with a huge buttonhole for the leg to come through). But most important, he has developed she broad-shouldered look he may well have begun a season ago. Then he started with football shoulder padding, since that was what he first found to use, scaling it down to wearable proportion.

"It is all activity, all the change in proportion around the top of the body that is the news," said Koko Hashim of Neiman-Marcus. Big shoulders and a tapering to the waist, a major theme in Milan, is guaranteed to be a popular silhouette with the French as well.

But there is another turn in the attention paid to the top, and it is in the decolletage for evening wear. There is expected to be much baring of the bosoms in the French collections.

Lagerfeld called it "a more self-conscious sexiness."

Broad shoulders often bring shorter skirts, warned Claire Pritchard of Lord and Taylor. "The proportion is simply better when you have width at the top to have a skirt around the knee."

As for the leather look here, "It's just evolutionary," said Neal Fox of I. Magnin, after yesterday's YSL fur show where there were several leather blousons and black leather trimmed in black fox for the evening.

"Leather gives a very precise look," said Leonard Hankin, touting one of its advantages and giving as an example the black leather jeans that showed up frequently in Milan.

"It is a natural way of protection," explained Marle-Pierre Tattarachi, one of the less well-known houses, which showed leather bras over knot dresses Wednesday. "There are big problems in the world . . . and when man is scared he starts to protect himself."

Claude Montana first shocked Paris fashion buyers six months ago with his black leather jackets that were called "Nazi," but which the designer called "romantic." Stores like Nieman-Marcus bought. Now even Saint Laurent has picked up the black leather scheme.

Meanwhile, designers have found a new way to brighten all the black and all the dull tweeds by using huge, obviously fake jewelry. "Only Farah (of Iran) could afford the originals," said Lagerfeld, who sometimes rests them like epaulets on the shoulder because they are so heavy.

"If someone bothers you," joked Lagerfeld, "you can take them off and use them as a weapon."

Saint Laurent and Kenzo, too, have said they are using big fake jewelry. "It's like a lamp on the clothes," said Lagerfeld.