More than ever in recent years, public television's "Dance in America" series -- a subcategory of "Great Performances" that made its debut in 1976 -- has been trying to nail down in permanent form those works and artists in American dance most deserving of posterity's attention.

The title of the series' latest segment -- "Balanchine and Cunningham: An Evening at American Ballet Theatre," airing tonight at 9 p.m. on Channel 26 -- further corroborates this aim. When you add that Mikhail Baryshnikov, artistic director of ABT, is also featured in the program as the male lead in Balanchine's "La Sonnambula," the intent becomes even plainer. Within the 60 minutes devoted to the venture, the viewer is treated to key works by two of the century's choreographic giants, performed by one of the nation's two foremost ballet companies, with the era's most exemplary male classical dancer in a principal role.

With all this going for it, the program nevertheless falls short of the unmitigated triumph it ought to have been. The account of Cunningham's "Duets" is superb from every standpoint -- the dancing and the televising complement one another so perfectly that the excitement of Cunningham's choreography comes across on the small screen almost as powerfully as on stage. In "La Sonnambula," however, we get less than half a loaf. Baryshnikov's acutely sensitive interpretation of the role of the Poet is now recorded for history. But even that performance is marred by serious shortcomings in other quarters -- most notably, miscasting of Alessandra Ferri in the crucial title role of the Sleepwalker, and the too jumpy, intrusive hand of director Thomas Grimm in the shooting and editing of the work.

Baryshnikov, in remarks introductory to "Duets," notes that it was his desire to be involved in the work of such outstanding American choreographers as Cunningham that led to his abandonment of the Soviet Union and his move westward in the first place. One of his early gestures in this direction, after his appointment as head of ABT in 1980, was to invite Cunningham to stage a piece for the ballet troupe. The latter responded by mounting "Duets," which he'd created for his own company two years earlier, for ABT in 1982.

Set to a percussion score by John Cage ("Improvisation III"), "Duets" is Cunningham at his spare, pure best. It's a wholly abstract essay in unadorned movement for six male-female pairs, in a sequence of overlapping, sharply linear duets that are like a network of electric vectors made visible. The incessant thumping and clicking of Cage's layered beats heighten the sensation of interlocking galvanic tensions. Grimm shoots the performance by a splendid cast head on, keeping the dancers in full figure, with a minimum of cuts. The approach lets the choreography speak eloquently for itself.

Admittedly, the challenge of "La Sonnambula" -- a narrative ballet with elaborate scenery and a large cast -- is very different from a video standpoint, and a mixture of distance shots and close-ups is imperative for storytelling purposes. The trouble is that Grimm goes overboard, sacrificing dance continuity in favor of dramatic clarity and impact. This is, however, a ballet, not a play, and a Balanchine ballet at that, which means that dramatic effectiveness is nullified if the choreography isn't treated as the higher priority.

Even if the video strategies were more sagely chosen, the performance would have been in trouble on the dramatic side. Ferri not only lacks the technical finesse the Sleepwalker role demands, but is entirely off track expressively -- all flesh and blood instead of ethereal wispiness. The key passages -- for example, the muted torment of her backbend just before she steps over the Poet's murdered body -- fall flat. There's a lot more emotional transaction in Baryshnikov's scenes with Leslie Browne, as the Coquette, than in those with Ferri. The performance as a whole has many things in it that any ballet enthusiast would be loath to miss. Indeed, it's the good parts that make one regret that this unique slice of Balanchiana wasn't more consistently realized.