Despite a wholesale reshuffling of Saturday's two concluding programs Joffrey Ballet at Wolf Trap, necessitated by a dancer's injury, the troupe still managed to provide one Washington premiere -- Majorie Mussman's "Random Dances" to a commissioned piano score by Jonathan Hancock. The work was originally performed by the Joffrey II company in 1979, and was added to the senior company's repertoire this year.

A fluid succession of numbers for seven dancers, the piece oscillates between playfulness and windswept lyricism in an atomosphere suggesting the romantic camaraderie of Jerome Robbins' "Dances at a Gathering." The language is basically classical, though in one male solo, for example, there are also allusions to jogging and shadow-boxing.

Both the ballet and it vaguely jazzy music, cast in the form of variations, are pleasant enough, but inconsequential -- bland echoes of material better served in other works.

A repeat performance of Joffrey's new "Postcards" on the devening program underscored the taste and graciousness of its choreographic details. As a whole, however, it still seems very much a ballet in search of an idea.

Back-to-back performances of Choo San Goh's "Momentum" on both the matinee and evening programs doubly confirmed the work's tensile strength and poetic fecundity. The choreography seem to well up from the music -- Prokofiev's First Piano Concerto -- as naturally and inevitably as sap from a vine. Madelyn Berdes, James Canfield, Beatriz Rodriguez and Mark Goldweber were particularly incisive in the evening performance.

In these and other works by Arpino and de Mille, the company managed to retain its vim and sparkle in the face of searing heat and won ample gratitude from both houses (last night's crowd numbered more than 5,500).