It's the great daydream of the stage:

The star falls down, gets drunk, has a heart attack, elopes, dies . . . Panic backstage: two hours to curtain time! . . . And the manager rushes up to you, back there in the chorus, and his hair is mussed, his eyes wild, his cigar sweaty . . . "You'll have to do it, there's no one else, someone find a costume for the kid . . ." And you go out there, heart racing but down deep a great calm. . . .

And you kill 'em.

In ballet it's no daydream. People get injured all the time. By the end of a long tour you're apt to see a lot of the third cast onstage, from the soloists on down. Besides, with the American Ballet Theatre it's a policy now to bring up young dancers and give them big roles. It does happen.

Thursday night 22-year-old Cheryl Yeager danced the starring part in the third movement of "Concerto," a Washington premiere. It is an exhausting series of jumps and turns, a spectacular piece, excruciating for anyone trying it on the infamous hard floor of the Kennedy Center Opera House.

She had danced it before, in Miami. There was an injury, and someone stopped Yeager during rehearsal the next day: "We're giving you two day to learn it."

"I wasn't even working on it," said the slight, dark-haired and poised young dancer, who was taking a few minutes off from her daily eight hours of practice. "The hard part is that you have to build up your stamina for something like that, and you can't do much about that in two days. It was the hardest thing I've ever done."

It happened another time in her four years with ABT, another injury, another hurry-up call, a week of frantic rehearsals of Cupid's little solo in "Don Quixote." No dancer dwells on those things -- "It could happen to me, too, of course" -- but just the same, there is that daydream.

Yeager comes from Bethesda. "Yep, I'm definitely local," she laughed, slapping a rock-muscled thigh. At 4 her mother took her to the usual little-girl ballet school. It was just part of her life. When she was 14, a freshman at Woodward High, she realized suddenly that she was going to be a dancer, had always been going to be one, wanted nothing else. She studied at the Maryland School of Ballet in Bethesda, later moved to New York to attend a special high school when she won a summer scholarship with ABT.

The first sign of something special came when she was 17 and was asked to stay on through the winter, with a subsidy.

"Then they had a cattle call audition to join the company itself," said Yeager, "maybe 150 people, a lot of them in the scholarship program, and I just went. I didn't think I'd get in, I wanted to get the exposure. But . . ." shrugging: a throwaway line . . . "They picked two of us."

Traditionally, ballet has rigid notions about what kind of dancer can do the various famous roles. A petite Giselle type can't possibly dance the elegant Swan Queen, for instance. But Mikhail Baryshnikov is changing all that at ABT, bringing up young people from the corps and trying them in a variety of roles.

Just this week Yeager was chosen for a pas de deux in the new version of "Swan Lake," and Tuesday night she appeared in another duet in "La Fille Mal Gardee." That makes three Washington premieres she is being featured in. She's not the only rising young dancer in the company by any means, but she is certainly moving fast.

It's a life that leaves little time for anything else. There are no men in Yeager's life. "Where would I meet them?" she says. Baryshnikov electrifies the whole company with his energy and drive, often taking rehearsals himself, demanding concentration, demanding dedication, demanding everything.

What does it feel like, striding out there: all those faces in the dark, those intent eyes, that expectant silence?

Before, when I'm standing in the wings, I look out and I think: 'Oh-my-God!' But the minute I start, I'm okay. There's so much to think about, technique, pulling your weight forward, getting the hand just right, all the things people have told you. You don't have time to be nervous. You try to enjoy it."

It takes time to come down. Yeager's mother, Rita, a grants technician at NIH, said Cheryl and her roommate, dancer Nancy Collier, who stays at the house when in Washington, go on a cheese-and-cracker orgy for an hour or so after a performance before they can go to sleep. Dancers don't have to worry about their weight as long as they're working. The routine of daily dance class, warmups, three or four hours of rehearsal -- a 12-hour of nonstop exercising -- burns up mountains of cheese and crackers. Her feet are always blistered, always hurting. She is losing another toenail.She had thought the blistering would stop in time, but no, it never does.

None of the other Yeagers dances. The family doesn't know quite where it all comes from. Her father Morris is a developer. Her brothers, Stuart, 20, and Michael, 15, are still in school. They come to all her performances. They are thrilled. And maybe just a little bewildered.

Not Cheryl Yeager. In the third act of "Concerto" she darted onstage smiling as if she were in her own living room, and twirled and leaped with easy precision, landing always with a dainty touch that is already her trademark. Tiny against a background of male dancers, she flowed, sleek and bright as running water, and then spurted away to a cascade of applause.