As might easily have been anticipated, the high point of last night's opening program by the Dance Theatre of Harlem at the Kennedy Center Opera House--with the company looking generally in fine fettle--was the Washington premiere of "Les Biches," Bronislava Nijinska's daring 1924 ballet about sexual antics of the leisure set.

The ballet was reconstructed for DTH earlier this year (as last year for the Oakland Ballet) by the choreographer's daughter, Irina, and dance notator Juliette Kando, and dance enthusiasts everywhere will remain much in their debt. "Les Biches" has had scant exposure in this country since the '30s. Yet it was one of the key successes of Diaghilev's Ballets Russes, an important forerunner of contemporary neoclassicism, and, along with Nijinska's other surviving major work for Diaghilev--the profound and revolutionary "Les Noces"--it is a source for the modern view of Nijinska as one of the greatest choreographers of the century.

This was my own first encounter with "Les Biches" in live performance; after so much reading about it and studying of still photos and sketches, the ballet on stage still turned out to have a vast capacity to stir astonishment, wonder and delight.

Diaghilev himself commissioned the score from the then 24-year-old Francis Poulenc; the impresario is said to have asked the composer for "a sort of modern 'Les Sylphides.' " What emerged was music in Poulenc's most typically wry, sweet-and-sour manner, suggesting quaint rococo ditties here, and cheeky music hall numbers there, spiced up at times with French popular song lyrics sung by a trio of vocalists (the DTH revival includes the singers, which hasn't been true of every past restaging). The decor and costumes were by Marie Laurencin--they've been exquisitely reproduced for DTH by John C. Gilkerson.

Nijinska's choreography brings these ancillary elements into perfect accord with her own conception. The ballet gives us a group portrait of young idlers casually on the make, at a house party in the south of France during the Jazz Age. There's no linear plot, just a succession of images and incidents, a gallery of types and individuals, at once redolent of a specific era and ajingle with echoes for any age and place.

During the orchestral introduction, Laurencin's front curtain shows us the caricatured outline of a young woman, surrounded by does (the French word "biches" means female deer, but is also colloquial for young women, somewhat like the American "chicks"). When the curtain rises we see an airy drawing room, perhaps in a beach house, with a large curtained window, a prominent blue sofa, a short stairwell and a foyer. Scattered around the room is a gaggle of flappers in light and dark pinks, with feathered caps. They dance with feigned hauteur, and break into body-shaking giggles; their steps are strictly classical, but they jut their shoulders forward, twist their hips and dip insinuatingly from the waist in unmistakably modern flirtatiousness. When they scatter from the stage, we get the sense of many other rooms in the place, with heaven-knows-what goings-on.

Everything about the ballet is faintly elusive, which is part of its charm. In the next dance we meet three muscle men in bathing attire, who preen and strut, as the flappers tease all around them, eventually chasing them over the couch. The strangest figure of all is a young woman in a blue velvet jacket cut off at the thighs, with a severe hairdo and an odd clipped gestural manner, strikingly portrayed by Virginia Johnson; she and muscle man Eddie Shellman carry on a desultory duet that ends in a lovers' clinch.

Also part of the scene is the Hostess (Lorraine Graves), who fidgets with her pearls and cigarette holder, and takes on the other two males almost as adornments. In another brief passage, two shy girls seal their attraction with an embrace, and then recoil in mortification. As the curtain falls, the place is literally jumping, with the whole cast on the go.

The DTH cast did a remarkably fine job of summoning up the special aura the ballet requires, coping valiantly at the same time with its by no means easy technical requirements. The company fared less impressively with the traditional stylistic and virtuosic challenges of their new "Pas de Dix" (from "Raymonda," staged by Frederic Franklin), though lead ballerina Virginia Johnson was superb, and Yvonne Hall and Judy Tyrus managed nice variations. What held the eye in "Firebird" was Geoffrey Holder's lush jungle decor and scintillating Stephanie Dabney in the title role.