What does Jane Fonda wear for her daily "butt tucks" and Rover's Revenge, two exercises from her best-selling books and triple platinum video?

"Something that will make me look good," she said on the phone from New York yesterday. Mostly it is a leotard with a belt, tights and leg warmers, but "if I'm heavier, I'll wear dark colors and something that covers me up more, such as silklike parachute pants and sweat pants," she said.

"If you like the way you look when you exercise it's an incentive," says Fonda, who will shortly bring out a line of exercise and related clothes. Her collection will be shown to store buyers in November and be on the racks of major department stores for the spring. Theoni V. Aldredge, who did the costumes for "Chorus Line" and another Broadway production, the soon-to-open "La Cage aux Folles," will create the clothes with Fonda under the Jane Fonda Workout label. There will be a logo, as yet undecided on, according to Aldredge.

"I opened an exercise studio that taught the things I wanted to learn, wrote the book that I wanted to read. Now I'm putting my expertise into a line of clothes I wish I could buy for myself," said Fonda, who describes the styles currently available as "plastic fashion." She added, "They are too shiny, too tight, too garish and lack class."

The dance clothes she admires are the more classic ones. "Not Flashdance-torn and ripped," she said, "but something innovative, made to work well for bodies."

She will bypass the current rage for leotards cut high over the thigh. "They don't support the buttocks." She prefers the more traditional cut which she then rolls up at the bottom to "flatter the hips." She usually wears a belt with her leotard, "to make me feel centered and conscious of my middle."

Beyond the strict exercise garb, Fonda and Aldredge will include clothes to be worn with leotards, such as wraparound dresses, sweaters and jumpsuits. In a small bag you could carry all the clothes you would need to wear from exercise class, to work, to dinner or to the theater, she said. "If a leotard is flattering I'll wear it to the theater. Why not?" All of her clothes will fill her two requirements--nothing should need ironing and everything must be union-made. Eventually there will be clothes for pregnant women who exercise and middle-aged women who don't. "Hopefully, they will encourage women who haven't exercised to think that they could," she said.

"My favorite clothes are things I've had for 15 years," said Fonda, not sounding much like the apparel entrepreneur she soon will be.

But she has already adopted the lingo. "I say things like 'interlock' and 'fabrics that are thirsty,' " she laughed. "My husband thinks I've gone nuts."