Bonnie Moore could be -- and most likely will become -- one of the great Juliets in Kenneth MacMillan's ballet version of "Romeo and Juliet."

She's already, at 21, far along the path, as she showed Saturday afternoon at the Kennedy Center Opera House, in the second of five American Ballet Theatre castings here. She's been dancing the part since last May, reportedly at MacMillan's insistence, and that was less than a year after her induction into the company.

It's easy to see why he'd want her. She's got youth, beauty and a slender, small-boned figure of virtually ideal proportion. All this nature has given her; talent, training and experience have done the rest. Though the company, wisely, is bringing her along slowly, she's already justified Baryshnikov's choosing her as his Odette in "Swan Lake, Act II," and I would go so far as to say that of the younger dancers now at ABT, Moore has the purest classical contour and the most far-reaching artistic potential.

Still, there's a long road ahead. It's interesting to compare her with Alessandra Ferri, who came to ABT even more recently (and whose Juliet I unfortunately had to miss). Ferri spent five years with the Royal Ballet; Moore came to ABT from the Washington Ballet, which is nothing to sneeze at but obviously a different proposition from the Royal. Ferri, with her singing, legato quality, her operatic projection and her dramatic temperament, is already a full-fledged ballerina. Moore is a ballerina in chrysalis, more inward and contained than Ferri. Her Juliet this weekend looked almost too self-sufficient, as if she didn't need a Romeo, only the idea of a Romeo (when Romeo took his leave after their wedding night, Moore emphasized that even he couldn't console her for his departure).

As far as Saturday's performance went, Moore shaped a slowly gathering crescendo of passion. When she was just dancing, as in her Ball Scene solo, or just acting, as in the second half of Act 3, she was near perfection. It was when both were required simultaneously that her portrayal seemed less well integrated -- sometimes when she's immersed in dancing, the character evaporates.

John Turjoman, her Romeo, is a young corps dancer who had good looks and posture, an unmannered style and a sort of brash innocence in his favor. But neither tragic dimension nor virtuoso blaze is yet within his reach in this role.

Like the other men in this cast, Turjoman had trouble with the treacherous sequences of traveling spins and jumps MacMillan has designed for the major male roles. Most put upon in this respect was Wes Chapman, substituting for the injured Johan Renvall as Mercutio. Chapman had the right cheery swagger but was uneven in the technical fireworks, except for his brilliant in-place pirouettes. John Gardner, in the less demanding part of Benvolio, made out the best technically.

Worth citing among other cast changes were Michael Owen, as an uppity, icily contemptuous Tybalt; Anna Spelman, as a distraught, but not excessively hysterical Lady Capulet; Kathleen Moore's dithery Nurse; Ty Granaroli's proper Paris; Elizabeth Laing's snooty Rosaline; and David Richardson's compassionate Friar Lawrence.