For two years Kim Cassidy drove longingly past the body-building club in her College Park neighborhood.

"I was dying to join," admits the 30-year old mother of three, who describes herself as "your typical athletically-inclined woman-a jogger and swimmer who was a pom-pon girl in high school.

"But I knew it was a men's club, and I was afraid of rejection. So I got some barbells to use at home, read lots of body-building magazines and bought short-term memberships at a local health spa."

Six months later, frustrated by the spa's dump vibrator-belt-type equipment" and "lack of instruction." Casidy finally called the Dynamo Barbell Club. Although they never had any women members before, they invited her to join.

"It was pretty isolating," she recalls. "I'd walk into the gym and there'd be a silence. There was no women's locker room, so I'd wear my gym clothes there, work out, then go home to shower.

"But it was so great -- like the graudate school of body building compared to the elementary school of a health spa. And in time, when they saw I was serious the guys became openly supportive."

In the two years since she first walked into the Dynamo gym, Cassidy has discovered "a growing network of women out there who are into weight-training. It's time we all got together."

From a "muscle magazine" article, Cassidy (who continued lifting through a "most successful" pregnancy) heard of a Florida-based women's body-building club: the Superior Physique Association, Inc.

She organized in May a Washington-area S.P.A. chapter with about two dozen members and is coordinator of Washington's first women's body-building competition -- The National Capital Women's Physique Contest -- set for Aug. 23 at the Shoreham Hotel.

Riding the crest of a new wave of interest in weight-training for women, the contest is one of a growing number of women's body-building contests across the country.

But belles have been featured recently in magazines from Sports Illustrated to Glamour. Even Esquire, that harbinger of male attitudes, paid tribute to women weight-lifters in their May cover story, "In Praise of Women's Muscles."

Bo Derek reportedly keeps her "10" breasts firm and high with a weight-lifting routine. Valerie "Rhoda" Harper keeps herself in a size 6 with thrice-weekly, 30-minute weight workouts.

This trend "is a statement about women of the '80s," says body-building champion Lisa Lyon, who trains at Gold's Gym -- Santa Monica, Calif.'s "muscle mecca."

"We're redefining beauty and femininity. In the '60s drug culture we were all emulating an emaciated Twiggy. But moving into the '80s androgynous culture, women need a new image.

"It's a kind of animal perfection," asserts Union's new National Physique Committee for Women, who at 5 feet 3 can bench-press weights heavier than her 105-pound body. "It's a vital, energitic look that proves a woman can be strong and still be beautiful.

"And if I have an hour to make myself look and feel better, you can be sure I'd rather be in the gym working out than sitting under a hairdryer with wet nails. This isn't cosmetic improvement. It's real."

Although the idea of women's body building gives some people nighmares of grotesuqe and female Arnold Schwarzeneggers, "Mr. Pumping Iron" himself says women's musculature and hormonal balance prevent them from developing large, bulging muscles.

"Working with weights doesn't make (women) look muscular," he writes (in "Arnold's Bodyshaping for Women"). "It only seems to emphasize all of their feminine attibutes, leaving them more beautiful, curvacious and appealing."

Rumors that some women take steroids to enhance their muscle mass "are pretty much unfounded," claims a prominent female body builder. "Women know that's dangerous and unhelathy."

One reason more women are lifting weights, says Joe Weider, publisher of the body-building bible, "Muscle and Fitness," is that "it's the only way to shape a body and fill out a figure.

"The only way to develop muscle, fill out weak areas and trim up flab is through resistance training. And who's to say it's unfeminine? Is a man who washes dishes unmasculine?"

The "overwhelming response" Weider has received since he began publishing articles geared to women has encouraged him to begin production on what he calls "the first magazine directly for women about weight training."

"Women's body building is finially taking its place as a sport," says Christine Zane, 31, of Santa Monica, a multi-title winner who spearheaded organization in October of the International Federation of Body Buildings first women's committee.

"It's been going on since the '40s," says Zane, who started body building in 1966 on her first date with Frank Zane, a four-time Mr. Olympia winner who is now her husband.

"But competitions then were run by men and were more like beauty contests. We've set up rules and regulations for the sport." Along with organization of the sport has come big money. The five top winners in the Miss Olympia competition, Aug. 30 in Philadelphia, will split $10,000 in cash prizes.

Says contest organizer George Snyder, "That's a big step up from $750," (the amount he offered the winner of the 1976 Miss Eastern United States contest).

Along with the money come pride.

"I used to be embarrassed to tell people I was a body builder," admits Stcey Bentley, 24, another Santa Monica resident who recently won the Wolrd's First Couples Body-Building Championship with partner Chris Dickerson, the first black Mr. America

"Now I'm proud," says the 5-feet-1, 105-pound dynamo. She has an agent to market her talents for such TV shows as Merv Griffin and John Davidson. "It's great not to be a weak, helpless female."

Says Sandy Chaillet, 26, a Woodward & Lothrop furniture department sales manager from Alexandria: "Weightlifting gives you confidence in yourself. You don't have to run and get a man everytime there's a tough jar to open (or a sofa to move)."

"I've got more energy, better skin tone and I've lost weight," adds her lifting partner, Yvonne Heiser, 20, who was a finalist in Tramps' Miss Georgetown Bikini Contest. "I know I look good and feel good."

Chaillet and Heiser currently work out 90 minutes a day at the European Health Spa and other area gyms to train for August's Washington contest.

"Some people don't beleive it when I tell them I lift weights," says Chaillet. "I usually keep a low profile, but one night in a bar a guy challenged me to arm wrestle.

"I tried to talk him out of it, but he insisted. I beat him in 5 seconds flat, got up and walked out. Last I saw him, his mouth was hangng wide open."