A COMPANY in transition -- that was the prevailing impression left by American Ballet Theatre on the last lap of its three-week Kennedy Center Opera House engagement, which comes to a close tonight.

ABT gave its first performances under its new artistic director, Mikhail Baryshnikov, in Washington just last December. Since then, the company has not returned to its home port of New York except for brief refreshment. The interim has been spent on the road, with a heavy, transcontinental touring schedule.

It's hardly surprising, then, that there have been no earthshaking changes since ABT's last visit. Indeed, it's rather a wonder that the company has managed -- enroute, so to speak -- to add five items to the repertory, and to mount two other novelties once it arrived. All of these acquisitions, however, are "restorations" of one sort or another; none is, strictly speaking, "new," except to ABT and to Washington.

By far the biggest alteration in the repertory was in many ways the least conspicuous. This was "Swan Lake," in what might be called a "semi-new" version by Baryshnikov, introduced for the first time at the Kennedy Center with virtually no fanfare. It's no secret that Baryshnikov would like to have an entirely new production of the ballet, given the money and time to get one together. Lacking both, he has instead begun tinkering with various aspects of the old production (1967) by David Blair, as he had already done with "Giselle" and "Les Syphides." The idea, one supposes, was to at least partially reinvigorate what was threatening to become a musty relic, and to get a running start on a wholesale revision. It's a good idea, and it has had some welcome consequences, but on the whole "Swan Lake" in its present pro-tem state has a decidely piecemeal look, the old sets (by Oliver Smith; worn, but still beautifully conceived) and costumes (by Freddy Wittop; ready for the junk heap) and parts of the old staging clanking uneasily against the Baryshnikov retouchings.

"Swan Lake," nevertheless, was the occasion for a performance that was not only a highlight of the season, but one of the most memorable ABT portrayals ever. This was, of course, Baryshnikov's American debut in the role of Prince Siegfried. "Swan Lake" is conventionally thought of as a ballerina vehicle -- its performance history has been dominated by the dual part of Odette-Odile. The ballet, however, isn't called "The Swan Queen," and even a cursory examination of its dramatic content makes clear that it is at least as much Siegfried's story as hers -- it is, in fact, a rite de passage, in which an impressionable and impulsive young man learns the meaning of true love through tragic error. Baryshnikov, like other male dancers who have been intrigued with the role's possibilities, has given us -- in outline, at least -- a Siegfried interesting and complex enough to function as a genuine hero. And in so doing, he's provided a tantalizing glimpse of the regeneration that might occur once the new production is a reality.

As for the remaining added repertory, Balanchine's madly mysterious "Sonnambula" is a carry-over, so to speak, from Baryshnikov's recent sojourn with the New York City Ballet. Paul Taylor's idyllic "Airs," though it is the first work by this modern dance master ABT has performed, was staged earlier for Taylor's own troupe. The historic Nijinsky version of "Afternoon of a Faun" has returned to ABT in a new staging by Elizabeth Schooling. Kenneth MacMillan's "concerto" has been revived with new costumes by Santo Loquasto. The pas de trois from "The Guards of Amager" adds a welcome slice of Bournonville choreography to ABT's current holdings. The pas de deux from "La Fille Mal Gardee" is an effective showpiece from the Kirov Ballet tradition staged by Baryshnikov's compatriot, Diana Joffe.

Of these, it's interesting to note that "sonnambula," "Airs," "Faun," and the Bournonville excerpt were alike in revealing how dependent upon stylistic accuracy and interpretative authority such reconstructions can be. "Sonnambula" was thoroughly effective only with Baryshnikov in the role of the obsessed Poet. "Airs" succeeded through the musicality and rapport of the ensemble, but showed at the same time the sizable gap between balletic and modern dance training. Performances of the Bournonville trio disclosed the difficulty of transposing the feathery Danish idiom to an eclectic troupe like ABT; unexpectedly, it was Baryshnikov who had the most trouble scaling the barriers, despite his superlative technical equipment. "Faun," thus far, seems an honorable failure -- honorable in its rigorous search for authenticity and the respect paid to this still startling choreographic masterpiece. The failure in this case isn't technical either; the ballet needs an order of conviction and subtlety that eluded its main protagonists in both Washington casts (Gregory Osborne and George de la Pena).

Elsewhere, the casting of principals tended to underscore the present thinning of ABT's top rank, especially among the men. Aside from Baryshnikov, the only other male principals around were Alexander Godunov and Kevin McKenzie. Three of the female principals -- Cynthia Gregory, Magali Messac and Martine van Hamel -- are exceptionally tall and sturdy in build; they need big men. Godunov is stylistically mismatched with almost everyone, and McKenzie is too lean and emotionally distanced, for all his finesse, to be an ideal partner. All this made for rather troublesome pairings.

There were, to be sure, numerous excellent individual performances: One thinks, among others, of Danilo Radojevic, more polished and electrifying than ever in the opening night "La Fille Mal Gardee" duet; of Makarova and Van Hamel (Gregory too, reportedly -- I wasn't able to see her's) as consummate Swan Queens; Gregory as a chilling erotic Siren in "Prodigal Son." But Baryshnikov's new faces-new feet policy has been making one steadily more aware of the abundance of growth potential in the company's lower echelons. A prime example has been the flowering of Cheryl Yeager, who's had five major assignments this visit. Though, at 22, she's still in the corps de ballet, she's been dancing with ever increasing radiance. Petite, exquisitely proportioned, she lights up the stage like a sunbeam with her unabashed euphoria; her lightness, rhythmical precision and instinctively harmonious line are suited to a wide range of styles.

With the opportunities Baryshnikov has been affording them, many other dancers are uncovering unsuspected gifts and interpretive promise; a few that come to mind from recent performances are Peter Fonseca, Leslie Browne, Cynthia Harvey, Johan Renvall, Victor Barbee, Susan Jaffe and Chrisa Keramidas. Then there are those surprise moments when a dancer pops to the eye out of the mass, riveting attention with some undefinable personal sparkle. If you've happened to notice Michaela Hughes (formerly the jewel of the Feld Ballet) doing those bewitching embellishments of the head, hands and arms in the Grand Pas Hongrois of "Raymonda," you know what I mean.

By now we've seen ABT dancing at the Kennedy Center through two separate engagements under Baryshnikov's stewardship. In the foreground of the December season was a threefold emphasis -- on the refurbishing of classics, on a broad apportioning of roles throughout all ranks of the company, and on maintenance and enhancement of the ABT heritage. Activity in all three directions was again much in evidence this time around.Baryshnikov's objectives, moreover -- both major and minor -- have been clearly implicit in the castings, repertory and programming of this spring season, and some immediate aims have been handsomely realized. There remains, no less clearly, a vast distance between his dreams for the troupe and the present actuality. If, however, this inaugural season has been any guide to coming years, we are in for just the sort of creative adventure the ABT enterprise ought to represent.