Like most older staples of current repertory, "Giselle"-the quintessential emblem of the Romantic era in ballet, which premiered in Paris in 1841-has undergone innumerable modifications of content and manner since its creation.

By coincidence, Washingtonians this week have a chance to compare two far-flung realizations of "Giselle"-one live, one televised. At Kennedy Center, American Ballet Theatre's version, originally staged in 1968 by David Blair, has been on view the past two evenings. Tomorrow afternoon from 1:30 to 3, NBC airs a Bolshoi Ballet performance, hosted by Edward Villela and featuring Natalia Bessmertnova and Mikhail Lavrovsky as Giselle and Albrecht.

What's surprisiang is that the differences turn out to be relatively trivial, and the correspondences-especially in crucial details of choreography-quite close.

The first ABT performance Thursday night, with Cynthia Gregory and Charles Jude (a pricipal of the Paris Opera Ballet, making his American debut), was technically assured but emotionally unconvincing for the most part. So is the broadcast Bolshoi version, for vastly different reasons.

Gregory is not a very credible Giselle, and the reasons have less to do with her size-Bessmertnova isn't tiny, and Alonso, another great interpreter of the role who may well be Gregory's model, isn't small either-than with personality and dynamics. It simply doesn't wash to have the faint-hearted Giselle, the archetype of the susceptible innocent, danced as a robust sprotswoman, which is how Gregory, despite her dramatic wiles, made her look in Act One. Jude was an aptly attentive and virtousic partner, but his rather callow acting didn't help matters.

The only time the ABT performance seemed wholly on course was during the otherworldly scenes with Martine van Hamel in her masterfully chilling personification of Myrta, Queen of the Wilis.

Bessmertnova 38, is still an exemplary Giselle, all wraith-like delicaccy. A Lilliputian TV screen, However, not only diminishes her performance but rules out the projection of subtleties-one can see her stylistic refinements, but given the medium and its commercial breaks, one can't reallyu feel them.

There are production differences, of course, other than those due to camera intervention. The Bolshoi omits the superflous Peasant Pas de Deux, for instance, and there are monor deviations in music, dancing and mime. The similiarities, on reflection, aren't so mysterious: Both versions descend from a St. Petersburg production staged by Marius Petipa in 1872. The common parentage still shows. CAPTION: Picture, Natalia Bessmertnova and Mikhail Lavrovsky in the Bolshi Ballet's "Giselle"