There is a quiet revolution in the exercise studios today, a revolution of substance and of style. Studios are establishing "identities," a physical fitness personality that is geared for specific exercisers' tastes. One studio's philosophy might be based on dance; another might focus on muscle power or sheer determination.

But the studios don't stop there. Many are extending their ideas about fitness beyond the workout room and into clothing. And the fitness wear for sale at the studio reflects the workout philosophy.

Diana's Dupont Circle exercise studio has wooden floors and high ceilings. Diana Hart, who established the business, does not believe that exercise is a competitive sport. "Our basis is in the arts and cultural side of the city," she says. The neon "Diana's" sign that hangs in the window, done by a Washington artist, puts that principle out front.

Hart chooses to keep the workout at Diana's based on dance because, "exercise is supposed to be fun. Our clients come here to relax and get away from busy, demanding schedules. Some places go for the burn. We stay away from that, our approach is more careful. We do not do jumping jacks."

Tina Reiman, studio director at Body Design by Gilda on upper Wisconsin Avenue, emphasizes the Gilda approach: "Every exercise we do here has been approved by Gilda Marx (who began the exercise studios 24 years ago). Our programs are constantly changing. Gilda is always in touch with sports medicine doctors so that we can use the latest knowledge for strong positioning in the least harmful way.

"The big difference about Gilda's is the training we give our teachers. We have an instructor and a spotter in every class, and each one of them can talk about muscle technology in a way that helpe students, not talks down to them."

Gilda's program is designed to change the shape of the body, and Reiman sees students transformed. "Initially they want to trim down, but then the interest grows. Their clothes start to change as their bodies improve." The new form does not happen overnight, it takes time and energy. As Reiman emphasizes, "This is not a play place."

Subdued and simple, Somebodies is secluded on the lower floor of a Georgetown house. Somebodies' president, Pat McKenney, has a straightforward approach to exercise; she wants to provide her clients with "the best quality teaching and the best facilities for serious exercise." Teaching students to breathe properly can enhance the entire system and McKenney finds that this is the always a good place to start. Although the emphasis is on technical exercise, McKenney believes in mixing fun with the serious workout. "We want to relieve stress not only here in classes but we try to give our students breathing tricks that they can use outside class when they need to relax."

Pictured here are three new exercise looks, right out of the studios, and a fourth choice -- Ralph Lauren's classic exercise wear. CAPTION: Pictures 1 through 4, AT SOMEBODIES: Fuchsia spandex leotard with boatneck by Francois G. For Dance France, $36; charcoal tights by Gilda Marx for Flexatights, $10; wool and acrylic leg warmers by Francois G. for Dance France, $16; AT BODY DESIGN BY GILDA: white thin-strap Flexatard, $21; white tube pants, $27; rose belt, $4; acrylic leg warmers, $11.50. All by Gilda Marx for Flexatard; AT DIANA's: geometric patterned cotton and Lycra leotard, $34; cotton and nylon tights by Softouch, $14; AT RALPH LAUREN/POLO SHOP: Cotton unitard, $52; cotton blend workout panty, $17; cotton sweatshirt with zip-up collar; $68; cotton cable-knit leg warmers, $28. By John Bowden