When a ballerina's dreams collide with toil, doubt; Just Like Jenny, by Sandy Asher. New York: Delacorte Press. 148 pp. $9.95. (Ages 10-14.)

The perfect book for any young aspiring dancer, ''Just Like Jenny'' depicts the moments of exhilaration and sometimes agonizing trials of two talented teen-agers aiming for a career in dance.

Faced with a hard decision, 13-year-old-Stephanie tries to decide whether she is going to devote herself totally to dance, wondering if she is what her dance teacher calls ''one of the gifted and gutsy few'' who will break into the professional world.

Although she knows she would rather dance than eat, Stephanie's talent and dedication are clouded with self-doubt and a dependence on and secret jealousy of her best friend, Jenny, whom she has always admired.

As both Stephanie and Jenny experience some successes and hard knocks, their friendship is strengthened, and they learn about themselves, their talents, and each other.