Versatility was the keynote of American Ballet Theatre's first week at the Kennedy Center, which ended with yesterday's matinee and evening performances. The company chose to pack all its mixed repertory programming into the first week, presenting 10 ballets by eight choreographers; the remaining three weeks of the month's engagement will be devoted to evening-length works ("Giselle," "La Bayadere," "The Nutcracker").

The Sunday programs, consisting of ballets by Ashton, Balanchine and Robbins, made a persuasive case for the troupe's present strength-in-depth, and demonstrated as well how much the ballets themselves can profit from contrasting interpretations. As it happens, yesterday was the first day since the start of the run that ABT director Mikhail Baryshnikov himself wasn't dancing, and of the 19 leading and featured spots, only four were occupied by principal dancers, the rest being assigned to soloists and corps de ballet dancers. If the company was endeavoring to show just how widespread its dancing talent is, the point was trenchantly scored.

Outstanding among the role debuts were the performances of soloist Cynthia Harvey and corps newcomer Ronald Perry in Balanchine's "Theme and Variations" at the matinee. Both had occasional, understandable troubles with the exceedingly challenging choreography, but what you noticed wasn't shortcomings, but the warmth and expressivity of the couple. Harvey's dancing had remarkable assurance and amplitude. Perry, as her gravely courteous partner, experienced minor lapses of technique and placement, but his musicality and classic bearing were more than adequate compensations.

In the evening performance of the same work, principals Cynthia Gregory and Kevin McKenzie danced with spacious elegance in their individual variations. Together, however, they seemed tensely uncertain, a circumstance probably due to McKenzie's stepping in at short notice for Patrick Bissell.

Magali Messac scored a distinct triumph in her first account of the Siren in "Prodigal Son" last night, giving us an erotic predator all the more formidable for her darkly menacing demeanor. Danilo Radojevic's prodigal, also his first, needs more dramatic definition, but his dancing was spectacular and the duet with Messac truly electric.

Kristine Elliott was delightfully perky and Warren Conover suave and precise in the evening's "Les Rendezvous"; Lisa de Ribere, Gregory Osborne and Robert La Fosse danced a crisp pas de trois in the same ballet. In the afternoon's "Interplay," Johan Renvall was appealingly nonchalant despite some shaky moments.