In days of old, when only male gymnasts were exceedingly bold, the women concentrated on smiling and dancing their way through "Moon River" with just enough tumbles and twists to qualify the whole thing as sport.

Then a back flip on a balance beam changed it all. In 1972, when Russian gymnast Olga Korbut won an Olympic gold medal with that heart-stopping feat, the women's gymnastic world went airborne. Now you can't make a decent high school team if you haven't got Olga's flip in your bag of tricks.

"The tricks get more difficult every year," says Shari Mann, 17, of Potomac, Md., who is competing against 23 of the best gymnasts in the country at this week's National Sports Festival. "I just hope it levels off soon or I'm going to be in trouble."

Mann is being modest. As a member of the national team during the last two years, she competed all over the United States and as far away as Moscow. She is ranked 14th in the country.

Mann is one of the new breed of female athletes who rushed to gymnasiums after watching Korbut on TV. They weren't interested in dancing; they wanted to fly. The sport accommodated that new leap so well that now even Mann, who at 5-foot-5 is a relative giant in the sport, can compete without being penalized for not being petite.

"I have what they call a mature body," says Mann. While other gymnasts sit with worried faces, Mann is slapping high fives to one teammate or whistling for another between two fingers jammed in her mouth. Once, she would have been called a tomboy. Today, she is an athlete.

In gymnastics, that new athleticism has flowered well. But the charge toward the outer edge of what is physically possible, while still appearing effortless, has created new pressures on both body and soul.

"I got burned out on gymnastics and laid out for five months when I was 13," said Kelly Garrison, an Oklahoma gymnast who is back at the age of 15. Last night she won a gold medal for the all-around competition, which includes four events--the vault, uneven parallel bars, balance beam and floor exercise. Most who drop out don't come back; some who desperately want to stay are forced out by broken bodies.

"I've had operations on both my knees for torn cartilage," says Mann. In the last eight years she has sprained more ankles than many NBA players. The broken toes she won't even mention. "Everybody gets broken toes."

About half of the girls aged 14 to 17 in Wednesday night's first round of competition had ankles or shins taped, either to prevent injuries or because of them. A fault in a routine used to be embarrassing. Now it can lead to broken bones.

"Sometimes it does seem retarded to be doing flips on a piece of wood just four inches wide and that far (four feet) off the ground," Mann says, laughing. "You're always afraid, throwing a trick for the first time. But by the time you are ready to do them in competition, they are routine."

There are, of course, giant paybacks in this sport, including satisfaction earned by doing anything with finesse. Garrison, for example, already has had two parades in her honor in her hometown of Altus, Okla. Many elite competitors have traveled to places that most people will never see. Then there is the magic of that spotlight.

"I just like to perform in front of a lot of people," says Lisa McVay, 15, of Waldorf, Md. In the last two years, she has competed in Canada and Japan. To get there she has had to spend 25 hours a week in practice during the last seven years and so much of her parents' money they'd need a calculator to compute it.

"It's an expensive proposition to support a gymnast," says Dr. Dean Mann, Shari's father, who has already traveled this route with two older daughters.

"You have to give up a lot, practically your whole social life," says Shari Mann, who is usually packing for a competition while most of her friends are heading to the beach. "I think I see my coaches more than my parents."

Wednesday night her parents were in the audience to see Mann score rather poorly. A few flips misguided by quarter inches sent her off the balance beam twice. On the uneven parallel bars, usually one of her best events, she got a bad start mounting the bottom bar after a running somersault.

"This just wasn't my night," said Mann, who didn't seem any the worse for wear. "Things don't go right sometimes for weeks at a time, but you just keep plugging." GW's Brown Leads East

INDIANAPOLIS, July 29 (UPI)--Michael Brown, a sophomore at George Washington University, scored 25 points and set a National Sports Festival record with 18 rebounds to lead the East to a 132-108 victory over the winless West in a men's preliminary basketball game today.

Johnny Dawkins, a guard from Mackin High School in Washington who will attend Duke, scored 17 points for the East. Andrews Sets 2nd Record Special to The Washington Post

INDIANAPOLIS, July 29--Theresa Andrews won a second gold medal with her second meet record Wednesday night as nine more swimming records were broken at the National Sports Festival.

Andrews, 18, of Annapolis, Md., swam the women's 200-meter backstroke in 2 minutes 17.68 seconds, breaking the mark of 2:19.64 set by Mary Wayte in 1981. Andrews won the 100-meter backstroke Tuesday night in a meet record 1:03.88.