I'm 37 years old, squatting on a blue plastic mat, feeling awkward as a toad. Hands planted on the floor, I push up with my legs -- nothing happens. "A little harder," comes the encouraging voice of instructor Fred Rodney. I sho-ove again, keeping my head tucked under -- and over I go. I've done a forward roll! "That's it," Rodney exclaims.

I feel as if I've just climbed Mount Everest.

Across the gym, a wiry, pig-tailed 12-year-old (my daughter) stands poised at one end of the balance beam before launching herself into a graceful back handspring, landing neatly on the beam.

What am I doing here?

Like most members of this class in gymnastics for grownups, I was here at the gym already, chauffeuring a carpool of kids to workouts and team practice. I agreed with several other mothers that I'd like to learn more about what my child is doing.

But there is also a secret wish, formulated as we watched our children progress from backbends and cartwheeels to gravity -- defying moves: "If only I could move my body like that!"

"It's something I always wanted to do as a kid, and didn't, so why not now?" asks perky, blonde Carol Ornitz, with a bubbling laugh.

Even so, Rodney has to do some fast talking to get this fascinated but fearful mother signed up for the class. everyone knows, nowadays, that exerciase is for a lifetime: 70-year-old men jog and play tennis; 80-year-old women swim every day. But gymnastics seems the exclusive province of the young and the graceful -- a sport where girls soar briefly to eminence at 14 and are has-beens by the time they're old enough to vote.

It's not necessarily so, says Rodney. Sure, the competitive team coasch is aiming to train champions, but there's room in gymnatics for "a nice recreational experience. Everyone exercises, but not everyone tries for the Olympics. You can feel comfortable on the equipment, work it and not get hurt. It's just like swimming. Competitors clock for speed, but loating is also an element."

Of course, the approach is different with beginning adults from what works with beginning children. "You have to work with adult weight. A hundred and twenty pounds is a lot harder on the ankles than 40 or 60," Rodney comments cheerfully.

More than one gymnastics center around the Beltway is offering classes for adults. And, as at Northern Virginia Gymnastics Center in Springfied, where I am enrolled, the aim is simply stated as "overall conditioning, agility, co-ordination and flexibility," and learning to work "effectively and efficiently with one's body wight."

Out class of seven coansists of half a dozen "30-ish" women and Mike, a lanky, enthusiastic man in his mid-20s. Rodney, a mustachioed, paunchy man, limber as a seal -- who has coached at several area gyms -- instructs the class gently, with a running patter of jokes woven into his explations.

We roll our heads -- around, down and back, flex our wrists, rock on all fours, extend arms forward -- with a reminder to keep elbows straight, arch our backs and lower to "ladies' push-up position." Out legs are stretched into as wide a straddle as possible; Rodney reminds us to point our toes. These warm-up exerciees, which start each seesion, are not just conditioning calisthenics but components of actual gymnastics skills. Silly as we feel, each move we learn is transferable to a piece of equipment, he assures us.

In successive sessions, we sashay up and down the floor, ignoring the girlish gigles of young gymnasts. Practicing a "donkey kick" -- hands on rhe floor, legs thrusting up behind us -- we tell each other, "That didn't look bad at all." ("Don't worry about looking like a klutz. You wouldn't be in this class if you didn't feel like a klutz," consoles Rodney.)

We learn to fall. "Jump, go down to your knees, arms halfway up, fall forward -- but into push-up position, not on your face!" Bursts of hilarity punctuate the class.

Varying the pace, we find the trampoline is everyone's favorite. (Though trampoline events are no longer part of competitive gymnastics, trampolines are used in many gyms to give the feel of moving in midair.) Rodney informs us that bouncing on the trampoline, arms rotating like a gently turning windmill, is actually an excellent exercise for cardio-vascular fitness. Jumping four minutes is the equivalent of jogging four minutes, he says -- and a lot more pleasant. After trying sustained jumping, we learn a minute is longer than it looks.

Back on the floor again, working on donkey kicks, I watch Carol Ornitz, 34, and pertite Nancy Dupree, 37, both mothers of two. They kick higher than anyone else in the group -- legs reach straight up in the air and hover a moment. This silly kick is the basis of a handstand -- a basic element in nearly all gymnastics skills. Trying it again, my legs rise a foot off the floor, wobble and land on the mat with a resounding thud. The need for exercises to strengthen wrists becomes obvious: They support a lot of weight in gymnastics by "feeling what they do, the idea of dealing with elements of the sport rather than skills or tricks."

Discouraged, I tell Rodney it would be nice to understand gymnastics by learning to do some move myself. He responds that dog-paddling is one element of swimming.

We line up for a "Rodney special" sequence. "Prance, run, jump, fall into a forward roll..." This time, I manage my forward roll on the first try -- for the second time since I was eight years old. As I wait another turn, I'm suddenly filled with a jumping-up-and-down squirming feeling -- also nearly dormant since childhood -- "I want to do it! I want to do it! It's fun!"

By daughter tells me it's embarrassing to see her mother making like a klutz during her workout. Why don't you drop out? she suggests hopefully.

Me quit? Not a chance. I haven't even gotten up on the beam yet! GYMNASTICS AT AN EXHIBITION

Friday night at 8 the University of Maryland Gymkana Troupe will put on an exhibition at the Chantilly High School gym. Tickets will be available at the gate: $1.50 for adults, 75 cents for children 5 to 12.