The horse's stall was empty. He had been taken to the vet earlier that morning. The gelding, named Professor, once earned $200,000 at the track for a man who later left him to starve to death. Now Professor was sick again. His new owner, Dede Doughterty, was not sure he'd make it this time.

Dougherty, a nationally ranked equestrian rider and recognized judge, had been through this before with a horse "that could have gone to the Olympics. That's what hurts, all over."

Stephanie Willim, Dougherty's youngest student, stared at the hay under her feet. She had heard this story before.

Two years ago, Willim was involved with a different kind of horse -- the kind used in gymnastics. In 1977, she won all four individual events and the all-around championship at the AAU Elite Nationals.

She was then, said Frank Bare, the executive director of the United States Gymnastics Federation, one of the most promising youngsters the sport had ever seen.

In music, they are called prodigies. In sports, they are phenoms. "Stephanie Willim was phenomenal for her age and her point in development," Bare said. "Without a doubt, she would have made the world cahmpionship and Olympic team."

At age 15, Stephanie Willim is retired. An aching back, which one of the 11 orthopedists she consulted said might result in permanent damage if she did not quit gymnastics, made her a has-been before she ever got the chance to be what she could have become. And that's what hurts Willim, all over.

"I heard it from the first doctor and that was real sad," she said. "And then seven or eight more said the same thing.

"I didn't want to stop," she added. "But I'd rather be safe and not paralyzed than anything else."

Contrary to the natural course of human events, athletes seem to be getting younger all the time. "The phenomenon of the teen-age athlete is comparable sociologically and psychologically to the 1930s and 1940s idea that you were going to make your child a movie star," said Dr. Arlene Kagle, special consultant for adolescent services at Community Research Applications in New York.

"This is not a new piece of the American character. The notion that any child can be president has always existed in this country."

For some, like the brother in Goodbye Columbus, who spent hours in his room replaying the record of his last basketball game, this dream can be difficult to give up.

But gymnasts are by nature flexible, and youngsters resilient. Greg Weiss, Willim's former coach at the MG Gymnastic Club in Silver Spring, said, "She's had standing ovations from 15,000 people. Making the transition from the pedestal to where she is, to a normal kid, working hard at horseback riding, is a very difficult thing and she has made it beautifully.

"Just to get back to normal kid status, to not think of herself as washed up, that's a tremendous success story."

Willim, who seems to excel at being normal, says, "I was a snobby brat. But I'm not that much anymore." She says she likes doing all the normal things, like "going to the mall and shopping and flirting with the guys." When she was a gymnast, there was never time for that. (SECTION) he hopes to make the Olympics one day as a rider in dressage competition.

"Stephie needs to believe she can do this," said Dougherty, her sponsor as well as her coach.

"Maybe she is reliving the gymnastics," said her mother, June Willim. "She's got a better chance this way. She's got 40 years to do it instead of 15."

In dressage, unlike gymnastics, competitors have been known to survive their 20s and even into their 60s. Even though she began riding just a little over a year ago, Dougherty says, the Olympics are "a realistic goal in terms of talent. It is something Stephanie can attain."

"She's done five years in a year," said Dougherty, who has competed at the Grand Prix level. "With the right horse she could perhaps ride at the second or third level now (there are eight). But I'm keeping her back."

Dougherty understands that Willim "can not afford to lose again, I want her to enjoy this," she added. "I don't want push to come to shove."

Dougherty entered her in her first show last fall. "I wanted to see how she would take it that she wouldn't win," said Dougherty. "She was fine. She understood."

Stephie remembers only that "there were a lot of horses" and that she "could hardly post right. I went around three times on the wrong leg," she said laughing. "I was sooo embarassed."

Dougherty wiped a wisp of hair away from Willim's face and added, casually, that she probably would have won the class if she had been on the right leg.

She will enter three more competitions this fall.

Willim's mother and coach are understandably anxious to avoid making comparisons between horseback riding and gymnastics, which might create unfair expectations. Sometimes Willim makes them herself.

"Dressage," she says, "is like a floor exercise. You steer the horse in different directions through a pattern. It's very dressy, very elegant."

Dougherty says Willim's training as a gymnast has helped her as a rider.

"She has innate balance," she said, and in dressage, balance and positioning are the key to getting the horse to do what it should do. But Dougherty has had to teach her how to use her muscles differently, to turn her legs in rather than out, to relax her back rather than arch it.

Dr. John Langloh, Willim's orthopedist at Georgetown University Hospital, says horseback riding poses no problem for her back because it does not put pressure on the lower spine, where she has her problem.

According to Dr. Langloh, Willim's condition "is called spondylolithesis of the fifth lumbar vertebra, which means that it is not connected in the back anymore. It's slid forward a little bit. When that happens, it's impossible to do the things you have to in gymnastics.

"In a baby, the condition can be congenital," he said. "In an athlete, it may be acquired through stress."

Dr. Douglas Jackson, director of the sports medicine clinic at Memorial Hospital Center in Long Beach, Calif., has found that spondylolithesis is "more common in young athletic women than nonathletic women and much more common in girl gymnasts than nongymnasts." He estimates that "2 to 5 percent of all female gymnasts" may have the condition, though many can continue to compete.

In Willim's case, her mother said, "11 orthopedists concurred" that she had to quit gymnastics. "They also told her she can do whatever she wants, as long as it doesn't hurt.

"When she got off the plane from seeing Dr. Kerlan in Los Angeles -- the 11th orthopedist -- I took her from the plane to the pool," June Willim added. "They all said swimming was good for this.She jumped in, had five private lessons and was winning medals in June."

But swimming was "too hectic," said Willim, "all this pulling and straining on the back. Diving hurt my back like anything. Tennis. I liked tennis, but I didn't feel like I wanted to do it."

Then, one day last spring, a friend brought her to Windcrest Farm, a private breeding and training facility in Clarksburg, Md., owned by Dede Dougherty and her mother, Louise. Willim had read "every single horse book in the elementary school library" when she was little, including "Black Beauty" eight times, but she had never ridden except "at fairs where they put you on a pony and walk around like that."

As a gymnast, Willim had not been allowed to ride a bike, much less a horse. Now, she says, she likes horseback riding "exactly equal" with gymnastics.

"What if the doctor says you can't ride anymore," she was asked.

"I'll kill him," she replied.

Willim eagerly led her visitor around the stable introducing its inhabitants. There was Ernie, who finished 15th in the 1968 Olympics. And Bear, who has a metal plate in her knee and "doesn't like short people because she thinks kids are going to tease her."

Willim, at 4-foot-9, is an exception to Bear's rule. She took her first lessons on Bear last summer. Willim led the way to the paddock to see the horse she now rides, aptly named Star. She confessed that she has gained 20 pounds since she quit gymnastics, a source of some embarassment to her.

Willim, whose freckles only come out in the sun, was asked if she is ever afraid.

"I've fallen off and it wasn't bad at all," she said. "Star bucked me off on that hill right over there. I know how to land, how to fall. It doesn't scare me at all."

Still, her mother says, "She's got one more fall to knock it (her vertebrae) out of position. When it starts to hurt, some work will have to be done on it."

If her vertebrae slip far enough, Willim would have to undergo a spinal operation. That operation would not affect her movement, or riding capability, after normal rehabilitation.

Her mother does not like to dwell on the past.

Gregg Weiss, who calls June Willim "the world's No. 1 mother," says, "the whole thing was harder on June than anybody. Stephie's young. It's easier to get acclimated."

June Willim says she "does not want sympathy for Stephie. I want her to stand on her own two feet and do what she wants to do."

Willim no longer looks at her gymnastics scrapbook.

"Mother has put it away," said Mrs. Willim. "Gymnastics are put away.

"Stephie still keeps the trophies and medals on the wall," she added. "But she'll put them away as soon as she starts getting the ribbons."

Her daughter still receives letters from more than 300 pen pals, some of whom, Willim says, "invite me to meets. It's kind of sad. I don't want to go back and watch."

She does go back to MG's Gymnastics Club where she trained for four years with Greg and Margie Weiss, who have remained close to the Willims. Their youngest child is June Willim's godson.

Last week, Willim went to show them her new saddle, which was paid for with money remaining in the gymnastics fund they had raised for her. It does not bother her to be there, she says, "until they start working out." v. illim, who once could do tricks that no one else in the world could do -- a full twisting Hecht back on the even parallel bars and a switch leg aerial on the balance beam-- says, "The only thing I can still do better than anybody is a handstand. I'm not supposed to do hardly anything except handstands. They don't put pressure on my back."

Willim is friends with Jackie Cassello, who now trains with the Weisses and is considered one of the top gymnasts in this country.

"We talk," said Willim. "I know what she's going through. She gets two weeks off to see her parents once every four months. I couldn't take that. Sometimes they forget you're a kid."

Although she does not often watch gymnastics on television, Willim has kept up.

"One girl ran away from home because there was too much pressure," she said. "One went down to 83 pounds," and another "got her ankles all messed up from too much vaulting.

"The only ones that survive are the ones that are mean. You have to say, 'No, I can't do that.'"

One of the things she is now discovering is that there is life after gymnastics. Last spring, Dougherty took her to the Middletown Horse Trials in Maryland. They stayed at the home of Lana DuPont Wright. Legend has it that the house is haunted by a decidedly friendly ghost, who insists upon cleaning up after unkempt visitors.

"I wanted to see if it was true," said Willim. "I hid my shoe under my pillow and threw my stuff all over the room."

In the morning, Willim swears, the room was clean. "It was real spooky."

Stephanie Willim may believe in ghosts but she does not appear to be haunted by them.