Ballet history doesn't repeat itself, but on rare occasions it gets a second chance. Last night at the Kennedy Center Opera House was such an occasion. As the opening gambit in American Ballet Theatre's gala benefit program, the company restored to life a ballet no one has seen on stage for 30 years, a work by a master that might never have been seen again but for some obscure symbols that lay undecoded in an archive.

The ballet was George Balanchine's "Symphonie Concertante," set to Mozart's violin and viola concerto by that title and given its premie re in 1947. Last night, as the fruit of a reclamation project begun last year and involving a number of scholars and ballet masters, the piece was danced again, in its ABT premie re, with Cynthia Gregory, Martine van Hamel and Patrick Bissell heading a cast of six demisoloists and a female ensemble of 16, and the Opera House Orchestra performing the music under the direction of Kenneth Schermerhorn, with soloists Nancy Ellsworth, violin, and Shelley Coss, viola. There was something a little spooky about the event, and not a little miraculous--unlike most other rejuvenated ballets, which issue from the memories of dancers, this one was staged entirely on the basis of marks on pieces of paper (signs of the written recording system known as Labanotation).

Was it worth the trouble? Not every Balanchine ballet is a deathless masterpiece, but the verdict on "Symphonie Concertante" is scarcely open to debate. It's hard to assess on a single viewing exactly where this opus stands in the rich Balanchine treasury, but it's assuredly somewhere way up high. Like the music that inspired it, the ballet evinces a magical fusion of outward simplicity and inner intricacy and depth. It would be difficult to think offhand of another known Balanchine work that confines itself more rigorously to the traditional academic vocabulary, without twists or quirks--the only thing that signifies its modernity is the extreme economy of structure. One is reminded of a remark by ballerina Maria Tallchief, who danced in the original production and "wondered whether Balanchine had done it as a learning exercise because there were no furbelows or frills. It was like taking your medicine every day."

If this is "medicine," though, it is surely of divine origin, a tonic restorative for the soul. The main choreographic framework takes its contours very directly from Mozart--the two female principals become the dance "equivalents" of the violin and viola; the lone male, who enters with the sublime second movement--the C minor Andante--supports both and each in turn, and the demisoloists and larger ensemble have distinctive "symphonic" functions answering beautifully to the musical score, yet without simple-minded mimicry. Gregory, van Hamel and Bissell, all three tall, strong and cleanly linear, seemed ideally cast for the work.

The stringent academicism of the choreography, its effects reinforced, perhaps, by the impersonal nature of the revival process, gave the performance a low-key, neutral aura. The humanity of Balanchine's choreographic statement, however, is likely to reassert itself gradually as the dancers settle into the ballet's interior with time. Theoni V. Aldredge's subtly adorned white tutus and David K.H. Elliott's unobtrusive lighting are splendidly in tune with the unadorned classicism of the production.

"Symphonie Concertante" was by no means the only triumph of the evening. ABT director Mikhail Baryshnikov returned to the Opera House stage last night in a performance of Balanchine's "Harlequinade" pas de deux, partnering the delightfully elfin Cheryl Yeager in a performance that reminded us once again of his transcendental powers as a dance artist. The duet is a gem of coquetry, ardor and wit; the technical fireworks were tossed off so lightly and casually by the couple that brilliance took a back seat to charm.

There was also a repeat performance of Merce Cunningham's dazzlingly ingenious "Duets," with Amanda McKerrow adeptly replacing Yeager in a cast otherwise unchanged from Tuesday night's Washington premiere of the work. Among other qualities that astonish in this piece, one noticed anew the unceasingly suspenseful rhythmic current, generated not by the music, but from deep within the dance fabric itself, a corollary, so to speak, of the self-transforming dance shapes Cunningham set in motion. Also repeated from Tuesday evening, with an identical cast, was Lynne Taylor-Corbett's carnival frolic, "Great Galloping Gottschalk," looking even thinner in substance on second look but unquestionably in firm command of its effects.