As opening nights go, American Ballet Theatre's entry at the Kennedy Center Opera House last night, launching a three-week visit, was far from bad, but it was also a long way from great. An erratic oscillation in quality was perhaps the evening's most conspicuous feature.

Part of the difficulty was the grab-bag character of the program itself: something modern, something traditional, something dramatic, something abstract, and so on. Ballet repertory programs are inevitably diverse in content; this one seemed especially diffuse. There were genuine highlights, and not a few of them. But too many things seemed out of joint to permit a fully satisfying composite.

On the gratifying side, much was new.Four of the five ballets presented last evening have been added to ABT repertory since the company was here in December, and they are, in general, strong acquisitions. Much in evidence, too, was a continuation of director Mikhail Baryshnikov's invogorating policy of spreading the dance action around to all corners of the company; as in December, corps de ballet dancers and those of soloist rank shared the limelight with principals.

Baryshnikov, for example, made his one appearance of the evening in tandom with soloist Cynthia Harvey and corps de ballet member Susan Jaffe (who made a storybook debut with ABT as a last-minute replacement during the company's previous opening night), in the new Pas de Trois from August Bournonville's "The Guards of Amager," staged for ABT by Stanley Williams.

Baryshnikov danced brilliantly -- does he know any other mode? -- but for him it was a relatively low-key effort, and in an idiom clearly somewhat alien to his own training. The "Bournonville style" -- along with the technique it involves -- is an elusive cluster of attributes, but only dancers reared from the start in the Danish tradition seem able to capture it wholly. Baryshnikov has the speed, the dexterity and the volatility required, but last night at least, he looked uncomfortable with the flightly rhythms, and almost too robust for the airy textures of the piece. The two women had their problems with the idiom as well, but their flouncy lyrical delicacy hit the mark. The piece -- it's only seven minutes long -- is charming, and will decidedly have its uses in the repertory.

The most impressive part of the evening was the company's splendid assimilation of another foreign idiom -- the modern dance language of Paul Taylor's superb "Airs," an even more difficult wrench in style for a classical troupe. Set to music by Handel, "Airs" indeed had classical aspects, certainly in its formal symmetries and elegant abstraction. But Taylor, like other modern dance choreographers, treats the body in a wholly different fashion from that of ballet. This is ABT's first attempt at a Taylor work -- "Airs" was actually begun as an ABT project a few years ago -- and last night's cast really got under the skin of the piece, despite sporadic troubles with the technique. The dancers -- Lisa Rinehart, Janet Shibata, Anne Benna Sims, Rebecca Wright, Brian Adams, Warren Conover and Robert La Fosse -- worked beautifully as an ensemble, and with a sustained musciality that underscored the idyllic harmonies of the design.

Also on the plus side was the engagingly flashy pas de deux from "La Fille Mal Gardee," newly staged for ABT by Diana Joffe, that so winningly showed off the sweetness and facility of Cheryl Yeager, and the sparky protechnics of Danilo Radojevic.

George Balanchine's strange, mysterious and offbeat "La Sonnambula," is, of course, a major new property for ABT. But it is also a ballet of extremely fragile moods, and unusually dependent on key role interpretations. Magali Messac's Sleepwalker, last night, simply lacked the fey, fugitive, spectral qualities without which the whole dramatic premise fails to materialize, and while Victor Barbee made a reasonably convincing Poet, he couldn't hold the tissue together by himself. Among the incidental pleasures were Gregory Osborne's diverting Harlequin antics.

The company's recently mounted "Raymonda Divertissements" concluded the program with lots of visual panache, but also with performances, including those of principals Cynthia Gregory and Alexander Godunov, that were patently uneven and uninspiring.