So much for the theory that convincing actors remain aloof from their roles. In American Ballet Theatre's only performance of "Fancy Free" at Kennedy Center this weekend, the three sailors on shore leave -- Kirk Peterson, John Gardner, and Charles Maple -- became so involved in their friendly fighting that Gardner received a cut on the face and Peterson a deep gash on his knuckles. Except for a brief exit by Gardner (presumably to wipe off some blood), the only unusual thing the audience noticed was the freshest rendition in some time of Jerome Robbins' perennial favorite about "Gobs and gals in World War II Gotham."

New York City Ballet has recently acquired this piece, dancing it with a sharp brilliance and acting it with an edge of caricature that completely misses the throwaway virtuosity and cunning portrayals of the knowingness and innocence of a former generation. With ABT not only the sailors and their leading gals, Rebecca Wright and Hilda Morales, but even the subsidiary characters of the bartender and passersby are accurate.

Also on Saturdays matineee Danilo Radojevic gave his first performance here of the title role in Eugene Loring's "Billy the Kid." Radojevic is a dancer who sometimes pursues virtuosity to the point of breaking all the rules of style. On this occasion, however, he gave an admirably controlled performance. His Billy, catapulted by his mother's death from curious lad to a killer astounded by his own actions, was an intensely pensive reading of the role. Lacking, as in Kirk Peterson's brilliantly mean Billy on Wednesday, was the quotient of charm that John Kriza gave to the part and that lends this ballet its legendary aura.