The trials of Cervantes' Don Quixote have become classic, but at the Kennedy Center they seem minor compared to the troubles of the dancers cast as Kitri, the heroine of the Russian ballet based on the Cervantes novel. In just over one week two ballerinas have had to be replaced in this starring role for American Ballet Theatre's brand new production.

First it was Martine van Hamel who seriously aggravated an injury on March 25. Gelsey Kirkland, the original Kitri of this version, finished the ballet for her that evening. Then Cynthia Gregory danced Van Hamel's subsequent performances.This weekend it was Gregory who became indisposed.

Kirti is a killer of a role. She is on stage in all six scenes of the full-length ballet, delivering high-voltage dancing almost every instant.

Gregory had danced Thursday night, Kirkland on Friday and at the Saturday matinee. Before the Saturday night performance, the Kennedy Center's Martin Feinstein stepped in front of the Opera House curtains to announce that two dancers - Marianna Tcherkassky and Cynthia Harvey - would replace Gregory.

Tcherkassky and Harvey don't look alike or dance alike, but it didn't matter. What brings life to Mikhail Baryshnikov's staging of this bravura ballet is a sense of excitement. Both at a moment's notice, were elated by the challenge and it sparked the whole cast.

Tcherkassky, a short and often gentle performer, came close to the fast, light, clear and continuous dancing that makes Kirkland so superb in the role. Quite originally, Tcherkassky gave hints of a dark pride within the vivacious Kitri.

Havey is a long-legged girl, just emerging from the corps. As the Kitri of Act 2, she had the chance to show the fine line of her dancing. As an actress she will surely have the chance to grow when she tries the complete ballet.

A repeat performance last night of Don Quixote" with the unusual double cast for Kitri was scheduled to conclude American Ballet Theatre's spring season here.