For all its neatly groomed structure and smooth execution, choreographer Jan Van Dyke's new "Variations on a Theme' epitomizes the most dismaying aspects of the '70s esthetic - a noncommittal elclecticism which says that anything can go with anything else and no principles (look at contemporary fashions in dress for a quick demonstration).

The new opus, introduced at a Jan Van Dyke and Dancers benefit performance at the Trapler Theater Saturday night, uses six of the troupe's eight dancers, in a bare feet and white studio togs.

The opening and closing sections (the "theme"), danced in silence, begin with regular formations that suggest a dance class. Steps, poses and combinations are set forth that are to become the basic compositional elements for the intervening five sections, each of which is performed to different music, ranging from disco, jazz and marching band styles to baroque and contempoary "pulse" music.

The idea seems to show that the same dance material can be given diverse new twists by varying the musical context. The effect, however, is only to emphasize the distressingly homogenized and sedated quality of Van Dyke's movement idiom. It's an idiom, with traces of ballet, Humphrey-Weidman technique, pop dance and other influences, of minimal dynamic modulation - it makes one feel the dancers' bodies are filled with cotton instead of bone, blood and muscle.

Van Dyke herself and Elly Canterbury were outstanding among the dancers. The program also included "Passenger" and Fleetwood Mac Suite."