Between the past weekend and last night, American Ballet Theatre introduced three new sets of lead dancers in "The Nutcracker," as the Mikhail Baryshnikov production commenced its second and final week of perfrormances at Kennedy Center.

Collectively, what this marathon of castings demonstrated was the resilience of the roles themselves; the polydexterity of the company (most of the leads were of soloist, rather than principal, rank); and the staying power of the production. It also showed how hard the ballet is, despite an easygoing surface - the smallest deviation in quality impinges moticeably on the effect of the whole, and the major roles are much tougher than they look.

Last night the parts of Clara, the girl on the brink of womanhood, and the Nutcracker who turns into her dream Prince, fell to Rebecca Wright and Kirk Peterson, both of them new to these assignments. At a first try, the pair worked bery well. Wright has a perfectly apropos wide-eyed sweetness about her, and her dancing, which has become steadily more impressive lately (her Amour in "Don Quixote= is one of the company gems), was nicely poised, especially in the difficult Sugar Plum variation. She'll want to cultivate a more fluent kind of phrasing in future performances. Peterson, a good match for her, looked a bit more uneasy. Technically solid for the most parts, he needs to concentrate on his princely posture and line.

As the Nutcracker for Saturday's matinee, Danilo Radojivic had two advantages beyond his own promising facility - Marianna Tcherkassky as Clara, excellent in the role she created; and conductor John Lanchberry in the pit. Radojevic's youthful brilliance was dimmed only by an upper torso tending to stiffness, and somewhat breathless phrasing.

Leslie Browne's Clara, Saturday night, was commendably lyrical, but dramatically rather pallied; Patrick Bissell, who has all the endowments for a superb Prince, hasn't yet measured the reach and tempo of the choreography to his own body.

"Nutcracker" is also a lot more than leads-the "supporting" roles are crucial, and there was much to admire all around. Warren Conover and Kristine Elliott as the Shepherds are one example of how a single variation can light up an entire act.