The most momentous thing about NBC's "Live from Studio 8H: An Evening with Jerome Robbins" last night was that it happened at all. Until now, classical ballet has been about as popular a subject for network prime-time as differential equations.

The rare exceptions have been grandiose specials featuring superstars and sure-fire warhorses, like the CBS "Nutcracker" with Baryshnikov, or snippets squeezed into variety shows between comedians and aquacades. Last night's NBC program was the first time in memory a commerical network has offered an American dance troupe (members of the New York City Ballet) in conspicuously American repertoire for a 90-minute stretch. For once the moguls were apparently counting on quality alone -- the genius of Robbins -- to carry the ball.

The show was a milestone from other standpoints as well, however. For Robbins himself, it marked a return to network television after a hiatus of some 25 years -- a concession by one of the century's outstanding ballet choreographers to the imperatives of the video age. And wonder of wonders, it was also a superb program. In the face of the hazards, built-in limitations and technical difficulties of televising live dance, the NBC production staff -- not at all experienced in dealing with this art form, mind you -- conquered the challenge brilliantly, with the help of some very exciting dancing. Somehow, the show managed to combine the technical refinement of prerecorded performance with the spontaneity and edge of a live presentation.

Director Rodney Greenberg and his colleagues proved extremely resourceful.

A sort of diffusion filter in the shooting of "Afternoon of a Faun," for example, gave just the right evanescent look to the ballet. An optical effect at the start of "The Mistake Waltz" substituted shrewdly for parting curtains. Overhead shots were cannily used throughout to reveal choreographic floor patterns.

As for the performances, there were too many highlights to cite them all, but among the most notable were the exquisitely sensual account of "Afternoon of a Faun" by Ib Andersen and Patricia McBride, and the buoyant sweep of a slew of principals in "Dances at a Gathering." Bravo Robbins, bravo New York City Ballet, and bravo NBC.