This is not about the graceful, effortless beauty of a group of people moving as one in sweet rhythms of dance. That will come later.

This is about young muscles quivering from exhaustion, about sweat that drenches leotards and glistens along long, outstretched arms. It's about preteens and teenagers listening, hour after hour, to the voice in the front of the room that relentlessly booms above the music.

"Somebody has a strange foot. Float your arms, Angelique. You can't do that at performance, Carrie. Don't look for it in the mirror. You can't see it; you have to feel it. Bend those elbows, baby. Bend 'em. Hold that arabesque, hold it. Eyes up. Put some kind of light in your face. Come on, come on, come on."

The voice belongs to Fabian Barnes, founder and director of the Dance Institute of Washington. He will soon be taking this group of children, most of them from the bleakest, toughest neighborhoods of the District, to the Concert Hall of the Kennedy Center for the Performing Arts.

The "Spirit of Kwanzaa" performances tomorrow and Wednesday will showcase the talents of children from five nonprofit groups that bring the arts to young people in the District. Barnes, who masterminded the show, has also included professional singers and dancers, including the Soweto Dance Theatre, which is making its U.S. debut.

In the weeks leading up to the show, students at the Dance Institute of Washington have been practicing after school until 9:30 p.m. every weekday and most of the day Saturdays.

Children in the junior company are as young as 4. Members of the senior group, which Barnes rehearses, range in age from 11 to 19. He drives them each night, he says, "past the point where they feel comfortable."

While they dance, he corrects. When mistakes he has corrected are repeated, he stops the music. Then he waits silently, allowing anxiety to build as he chooses his words.

"You are not performing. I feel nothing coming from you. You're going through the motions. Joseph, how tall are you?"

"Five-8," 15-year-old Joseph Bunn answers.

"Well, you have to look 5-11," Barnes retorts. "I know you're working hard; now work smart."

No one talks back or shows irritation. At the end of a grueling rehearsal, Amber Mayberry, 15, looks confused when she is asked whether she ever gets fed up, ever just wants to quit.

"I couldn't quit," Amber says. "Dance is my life. This is what I do."

Twelve-year-old Troy Boston, who also has a second-degree black belt in karate, says he can't wait to come to rehearsal. Troy's dancing career started after a visiting dignitary from the Kennedy Center saw him in a school play at the Marie Reed Learning Center in Northeast Washington and arranged lessons for him.

"We know Fabian is driving us harder and harder because he wants us to look good," Dionne Figgins says. At 19, Figgins is the elder statesman of the institute's senior company. Soon, she will move on to the Dance Theatre of Harlem.

When the dancers step onto the the Kennedy Center stage, Barnes says, they will be judged by professional standards. "I would be misguiding them if I allowed them to go out and not rise to the occasion. They need to put on a show."

But the performance, while important, is part of a larger goal.

"I am instilling the work ethic," Barnes says. "It will carry them through life the way it did me."

Barnes, the oldest of 10 children in a poor Seattle family, danced while many children in his neighborhood followed the lure of drugs, easy money, guns. Years of hard work led to solo performer status in the Dance Theatre of Harlem.

Then, after several summers teaching low-income children in the District, he decided to form a company dedicated to year-round excellence.

"A lot of kids in the inner city may not get any structure in their everyday lives," Barnes says. "I pass it to them through dance. They pursue something positive, and of beauty."

Like the dance institute, the other arts organizations preparing for the Kennedy Center show give children more than art and culture.

"These programs are about pride and self-confidence, about youth development and leadership," Barnes says. "They're also about drug, alcohol and pregnancy prevention."

The Spirit of Kwanzaa celebration begins at the Kennedy Center today, when the center and the Smithsonian Institution co-sponsor a workshop on the significance of the African-centered holiday. Smithsonian scholar James Early will host the free workshop at 6 p.m.

Local arts groups performing the next two nights include Step Africa, a gospel choir from the Washington Performing Arts Society, and the KanKouran West African Dance Company. A gospel choir from Houston Elementary School's visual and performing arts program will also perform, as will a musician from the Memory of African Culture Performing Company.

Donald Williams and Kellye Gordon, principal dancers from the Dance Theatre of Harlem, are among the professionals in the show, along with folk singer Donald Leace and jazz singer Esther Williams.

The professionals, Barnes hopes, will help draw larger crowds. But they also serve as models to the young people, who will be giving their all to the show.

Joseph, who is working to look three inches taller than he is, said he is getting increasingly excited as the hours move him closer to show time.

"There will be a lot of important people there, people who have been in the arts a long time," Joseph says. "I wonder what they will think of us? But no matter what, after it's all over, I'll still be dancing."

CAPTION: Joseph Bunn, 15, and Angelique Smith, 12, rehearse with other members of the Dance Institute of Washington's senior company for their Kennedy Center appearances.