It looks so smooth. A leap, a twist, barely a splash. Again. The form spins through space, hurtling 10 feet downward, effortlessly tucking and rolling itself, and then snapping I ramrod straight, like a satin ribbon flying in the wind. Maybe three seconds, maybe less. It's hard to tell.

When Susan Brown dives from the high board, time loses its measure and, for a moment, the world becomes a swimming pool.

And if coaches and pundits are to be believed, the Potomac 15-year-old with a body as sleek and taut as a swan's neck may someday have a chance to bring home the gold. The Olympic gold.

"When you talk about Susie you're talking about excellence," says her coach, Carl Cox, minutes after the last dives of the day have been completed at the Fun and Fitness Center in Arlington where she practices three days a week. "I've seen a lot of great divers, but Susie is among the best. If you asked me if I thought she could make it all the way, I would have to say yes.

"Einstein was a genius in math; Susie is a genius in diving."

When a coach praises a protege, suspicion is a fair reaction. But when some of the nation's best diving coaches, whose rosters have included some of the world's champion divers, come calling at the door, it is also fair to suspect one's suspicion.

Brown, who has been diving since she was 9, already has been contacted by coaches from Harvard, Ohio State, Michigan, Stanford and the University of Texas. And come February, she will pack her bags and head west for a year and a half of training, six days a week, under 1976 and 1980 Olympic coach Ron O'Brien in Mission Viejo, Calif. O'Brien approached Brown with a coaching offer this summer after he saw her place second in the United States Junior Olympic Age Group Championships in Irvine, Calif.

"That should tell you something about Susie's promise," says Cox, a coach at George Washington University who asked Brown to train with him more than five years ago after he saw her dive. "That man lives for excellence."

Off the board, Brown is like a lot of teen-agers, balancing between the worlds of teddy bears and diplomas, at times awkward, at times loquacious, at times giggly and at times inexplicably quiet. The Winston Churchill High student spars kiddingly with stepfather and coach and begs for quarters to play the video game in the corner of a hamburger joint not far from the swimming pool.

Little in her appearance or demeanor demonstrates that a monumental commitment has been made at such a young age. Her hair is streaked blond from chlorine, her nails are skin short and her complexion is as smooth and shiny as an apple in the last days of fall. She says she loves disco music and her boyfriend, a football player at Georgetown Prep. Diving, she says simply, is just a part of her life, like going to school and doing homework.

When an athlete can use her body as elegantly and surely as the last crisp line of a poem, it is expected that some deep philosophical reasoning underlies the action and that the motivation can be as easily articulated. But as Brown sits there in a booth, devouring a hamburger, two baskets of french fries and a cola and talking about the rock concert she attended the previous night, the inevitable question of why seems strangely out of place. She seems happy, normal, not at all serious. Saturdays, she says of her weekend practice, are "hazardous to health".

But still the question comes.

"I can't really explain it. I don't know why I do it. But I know that just about everything in my life evolves around diving. I'm always thinking about it.

"Two or three years ago, a couple of divers from around here went out to California. I can remember talking about that with some of my friends who were also divers and they couldn't believe that they were doing it. . . . I thought it was the best thing. It was sort of a joke dream I had that I might be able to go also. Now, it's like a dream come true.

"There was never any doubt in my mind that I wanted to go out there, to go to California. I didn't hesitate a minute to make up my mind. There is just something inside of me that wants to do it, that has to do it."

Brown first began diving at the Bethesda Country Club more than six years ago. She was watching the team practice one afternoon and asked the coach if she could join. He asked her what she could do. A racer's dive, she replied.

Since that auspicious afternoon, Brown's progress has reflected the quantum leaps women's diving has made in the last decade. She has qualified for the national championships every year since she turned 12 and this summer, at 15, she performed a "back 2 1/2" at the junior diving championship in Irvine. A woman first tried that dive -- two and a half somersaults executed from the back position on a high dive -- in international competition during the 1976 Olympics.

Both Brown's parents were at her side this summer -- as they are at most of their only daughter's meets -- when she spun her first successful back somersault. Walter Burdick, who has been Susie's stepfather since she was 1 1/2, and her mother Gloria say they will be sad when Susie leaves for California. They worry that perhaps she may settle in the sunshine state, but ultimately, they say, the decision was hers.

"Most of Walter's and my life have revolved around Susie," says Gloria Burdick. "But a parent can't continue to live life through a child.

"I feel very blessed for Susie, that she has a talent and that she has decided to pursue it. It will be difficult, really hard, but we can't hold her back. It's her decision."

Cox attributes Brown's success to more than just athletic prowess. Faith in her ability and motivation -- that sense the soul knows but the mind finds hard to define -- is what makes her a winner, says Cox.

"Even when Susie was young she was ripping dives that mechanically she wasn't really ready for . . . . But she wanted to do them. She was the type of kid that makes a coach want to coach them.

"She always believed she could do it and when she didn't win, she wasn't a crybaby. She would come back stronger.

"You've got to be motivated to attain excellence, and I've seen a lot of good divers who didn't make it because they weren't capable of the motivation. That's what it's all about, about being best," Cox continued.

"You've got to believe that you can be the best if you're going to be the best. Susie believes it."