It is not for the usual dance reasons that Jiri Kylian divides his company along sex lines for "Sinfonietta," the ballet that first brought this young Czech director of the Netherlands Dance Theater to prominence as a choreographer. Performed at Wolf Trap in 1978 as NDT's contribution to the program built on the music of Leos Janacek, "Sinfonietta" was danced again this weekend at Saturday's matinee.

In the universe postulated for this piece certain bodies, which happen to be female, fold in and curl up like plants sensitive to the absence of light. Other bodies, which happen to be male, provide the stimulus and propulson to counteract this "female" tendency to return to the pod. Watching Kylian's fascination with the lifting, carrying and sliding down that serve to hide or expose torso and limb surfaces in unexpected ways was the most rewarding part of a season that came close to being a one-man show. NDT, despite balletic roots, leans on the auteur concept as much as any modern dance troupe.

Good dancers, though, do count. The company as a whole is stronger than at its first Wolf Trap visit. The women no longer collapse when infolding is required. And, now, in addition to veterans Arlette van Boven and Gerard Lemaitre, there are at least two performers on whom the fans keep an eye -- Kathleen Fitzgerald with her fine placement and Chris Jensen with his concentrated turns.

"Dream Dances," a sort of international folksong fest, had duets, trios, quartets, even a solo -- but not to show off the dancers. Dominant was Kylian's attempt to expand his choreography by using diverse folk material. Results, though, were formalistic with an Italian ballo or an Azerbaijan love dance emerging as mannered as the traditional Chinese tea variation in "Nutcracker" minus the classic's varied steps.

Perhaps the texture of Kylian's works would profit if he lavished as much study on Bournonville, Petipa and Blanchine ballets as on the dances of the Australian aboriginals. From the evidence of his neoclassic combinations to Haydn's "Symphony in D" (which replaced "Overgrown Path" at the matinee) and even the volleys of jetes and tours for the fanfares in "Sinfonietta," a bigger academic vocabulary and the sustained linking and developing of chains of movement would help to enrich the often blunt statement of intriguing themes.