Marcia Frederick is a mere slip of a 15-year-old girl from Springfield, Mass, who recently became the first U.S. woman to win a gold medal in international gymnastic competition at the World Games in Strasbourg, France. Her Stalder shoot on the uneven parallel bars earned her a 9950 score. Two judges awarded her perfect 10s.

Perfect scores in gymnastics evoke memories of Romania's computerized Miss Perfect of Montreal, Nadia Comaneci. But Marcia's brown eyes turned cool at the hint of any similarity between the two. As any teenager faced with a prying adult, she sinks deeper into the downy security of her blue jacket and jams her fists in the pockets as if to hold back some inner turmoil. "I don't compare myself to anyone," she says.

The gold medal has produced the expected turmoils interviews, appearances and requests for exhibitions. Her coach, Muriel Grossfild, says Frederick's instant stardom has created no conflict within her American Gold Gymnastics team. "If anything, it has been easier now that it's clear (who's best). The girls fight among themselves, but they close ranks tight when someone outside says anything about one of them."

Ferderick seems totally unaffected by fame - oblivious to stardom. Her focus is not on what happened in France, not on today or even tomorrow. She has her clear eyes set on a bigger target: 1930 in Moscow.

But the way to the Olympics is paved with individual bricks, each marked with its "IF." A gymnast is a special brand of athlete, a thorough-bred who must have the right balance of strength and flexibility, the right combination of determination and discipline. A lifetime of hard work can be erased by injury, a new boyfriend and, in some cases, normal physical growth.

"After the games (in Strasbourg) a few Western coaches suggested that the East Germans and the Russians were drugging their girls to delay puberty, to keep them small-framed," said coach Don Peters. "But it's been my experience that the rigors of daily training and the low percentage of body fat on these pre-puberty girls simply detains the onset of maturity. I used to worry about it, but then I noticed that if one of them gets hurt and has to lay off working for awhile, then usually the normal adolescent growth starts up."

That's one large "IF" facing five-foot-one inch, 90-pound Frederick now. She's hobbling around on crutches, enduring physical therapy three times a week and forgoing work-outs in all her events except the bars because of a lame left ankle she first sprained last spring. She looks out of sorts as she watches her teammates limber up for the afternoon workout. She says she's had to watch her weight closely since her wings were clipped.

"I lost eight pounds in just one week," she said. "Sometimes I skip lunch. You've got to have discipline if you want to reach your peak before it's too late." She follows a Weight Watchers diet, as do most of the 11 other Elite gymnasts who board at Grossfeld's American Gold Gymnastics Club.

Her coaches and doctors promise that she'll be back full strength by January, but a two-month vacation is something to fear if you have your heart set on a gold medal with seven interlocking rings. She fills her extra time reading. Tolkien is her favorite author. As a hobbit collector, she describes gymnastics as a secret world of good against evil with its special language that spells out its magic.

Her eyes sparkle for the first time all afternoon. "Look," she says rolling the words together like a song, "you say glide - kip - forward - hip - circle - Stalder - full - pirouette - handstand - beat uprise - one - and - a - halfbeat - surprise - fall - Stalder - roll. Do you understand that?"

She paused and gave a soft sigh. "Nobody but another gymnast would. If you put that in an article, people will think your typewriter broke. That's a quarter of my routine on the bars, and even my parents don't understand.

"When you're doing a routine, your're in your own world. All you see is the bar in front of you or the space you're in. You're moving and moving all the time but you can hear yourself think. You can hear yourself talking, like, 'My foot's got to go here; then my hand there.' It's really neat."

At home in Springfield for week-ends, Marcia-the-Gold-Medalist turns into a typical teen-ager. She teases her 13-year-old sister, Carol, by jumping on her freshly made bed. She stays up until 3 a.m. talking with older sister, Peggy, 13, with whom she shares a room. She plays basket-ball in the backyard with her dad, Charles. "She drives me crazy trying on clothes," according to mother Christine.

Until Marcia is given a clean bill of health by the orthopedic surgeon in charge of her ankle, she'll have to content herself with "running the movements in my mind."

"Some gymnasts hate the beam and others can't stand the vaulting horse," she confided, her eyes still on the workout she was missing, "but I don't hate anything."