It was not one of your outstanding opening nights for American Ballet Theatre, as the troupe moved into the Kennedy Center Opera House last night for the start of a two-week run, with a program including Balanchine's "Ballet Imperial," Twyla Tharp's "Brief Fling" and Leonide Massine's "Gaite Parisienne."

There were minor exceptions and one major one ("Brief Fling"), but by and large it was just one of those seemingly unavoidable occasions in the theater when everything was under a pall, and little was quite up to the mark one expected.

One possible reason for the let-down has nothing to do with dance. As I write this, the U.N. deadline for Iraqi withdrawal from Kuwait is 30 minutes old, and it looks very much as if push is about to come to catastrophic shove. Deadlines concentrate the mind, but not, in this case, on ballet. We may need ballet more than ever, to help remind us of the reason, order, harmony and idealism human beings are capable of in the fullness of their creativity. But can anyone in the Opera House last night -- onstage, backstage, in the pit or in the audience -- have been unaffected by the terrible prospect confronting all of us?

Susan Jaffe, who was so stunningly in command of the principal ballerina role in "Ballet Imperial" when the company first brought it to Washington, seemed troubled from her first entrance, having totally uncharacteristic difficulty with sequences she'd made seem child's play before. Nor was she or the supporting ensemble ever convincingly immersed in the music or its dramatic implications. The workaday rendering of the Tchaikovsky score by the Kennedy Center Opera House Orchestra under the baton of Emil de Cou didn't help.

Still, the performance had some formidable rewards, mainly in the dancing of Amanda McKerrow as the second ballerina, reminding us, with her graciousness, sensitivity and style, of the expressive potential of Balanchine's choreography in this palatial work. Ricardo Bustamante, who partnered Jaffe, also danced splendidly, for the most part.

"Gaite Parisienne," a "period" charmer, always puts the company on a thin edge because the right balance of elements is so difficult to muster, and because a few key roles are so crucial to the effect of the whole. Marianna Tcherkassky, last night's Glove Seller, is one of ABT's veritable treasures, a dancer who is never the less than fine, a model of stylistic purity, and far more adaptable than most to almost any idiom or character. But sexy innuendo isn't her forte, and the part looked more studied than spontaneous last night. Danilo Radojevic danced skillfully as the Peruvian, but missed both the wit and the wistfulness of the role. There were estimable contributions from Guillaume Graffin as the Baron, Amy Rose as the Flower Girl, Veronica Lynn as La Lionne and Christina Fagundes as the lead Can-Can Dancer, among others, but they weren't enough to keep the performance from looking like a less than inspired run-through.

It was up to "Brief Fling" to redeem the evening, which it did handsomely. In this exciting, complex and ultimately mystifying opus, the cast seemed, not only fully charged up for the occasion in technical brilliance and authority, but at one with the ballet's expressive purposes from the giddy start to the disconcertingly somber finish. Cheryl Yeager, Wes Chapman, Kathleen Moore, Kevin O'Day, Jamie Bishton, Keith Roberts, Claudia Alfieri, Isabella Padovani, Gil Boggs and Robert Wallace headed the superb ensemble.