When Mikhail Baryshnikov parted the Kennedy Center Opera House curtains last night and strode out upon the stage apron in an open-collared shirt and jeans, anxious murmurs passed through the capacity audience.

Doubtless the first thought that popped into every mind was "Oh my, he's not going to dance tonight." The alarm proved false. Cancellation wasn't the purpose of this unexpected prologue to American Ballet Theatre's opening night "Giselle," at the start of the company's three-week engagement.

Baryshnikov stood silent for a moment as the whispers subsided, looking gravely at the floor. Then he lifted his head.

"The last few days we have lost two great artists, two men of the theater -- James Cagney and Erik Bruhn," he said, referring to the great screen star and the extraordinary Danish dancer, whose deaths followed so quickly upon each other. "Many words have already been said," Baryshnikov continued. "And I've got nothing to add. But we would like to dance this evening's performance in their honor, and for them. Thank you very much."

It was a moment of such authenticity and delicacy of feeling that the performance that followed was hard pressed to match its depth.

Despite its ad hoc character, the tribute also seemed peculiarly fitting to the symbolic nature of the evening. The art of Cagney and Bruhn defined the polarities of Baryshnikov's own career -- on the one hand, popular entertainment of an order so high that it enters the sphere of art, and on the other, art of such classic austerity that it sometimes seems to belong more in a temple than a theater. In a very real way, Baryshnikov follows in both their footsteps.

It was an evening filled with other such echoes. "Giselle" was the ballet in which Baryshnikov made his debut in this country with the company he now directs, and though much water has passed under many bridges since, the role of Albrecht is still one that reveals his transcendence as a performer as strikingly as any other. Dancing opposite him last night in the title role was Alessandra Ferri, who inevitably stirred memories of Bruhn's most celebrated partner in this same ballet -- Carla Fracci, another dark-eyed Italian beauty and the quintessential Giselle of an entire ballet generation.

Despite many felicities, last night's first act seemed rather emotionally pallid. Ferri made a charming Giselle, in an interpretation that had its distinctive side from her entering skip -- one of the heroine's signature steps throughout the act. Ferri's movement was large, open and clear with an unclouded buoyancy of spirit. There was no hint of the morbid or tragic here, no presage of her fate -- only trustful joy and exuberance. Still, the portrayal seldom went beyond the picture-book surface of the role, even with a mad scene of acutely impassioned melancholy.

As for Baryshnikov, he was an impeccable Albrecht in every outward respect, and he benefited from having a partner who is an ideal physical match. Yet he too seemed not fully engaged in the drama of love and betrayal that is "Giselle's" first act.

Almost everything changed for the better in the second act, starting with the music, which conductor Paul Connelly often rushed through earlier -- the opening orchestral bursts, for example, were faster, muddier, and hence less conducive to anticipatory excitement than any one can remember. Connelly was much more considerate of the romantic gloom of the second act, and everything that ensued on stage confirmed the company's deeper involvement. In particular, Martine van Hamel's Myrta bespoke greatness from her very entrance. She was always magnificent in this part (which she has not danced for some time now), but to her patrician implacability of old she added last night a new layer of pathos -- she was the mother of sorrows as well as Queen of the Wilis. The whole first scene with the Wilis, abetted by van Hamel's Myrta, the exceptionally strong Moyna and Zulma of Leslie Browne and Lucette Katerndahl, and the ensemble with its sighing sweeps of arm, was one of the high points of the evening.

Points as high or higher were to follow, as Baryshnikov and Ferri -- in this "dancing" act, as opposed to the more "acted" first act -- soared onto another plane of performance. Ferri looked uncomfortable with some of the adagio aspects of the choreography, but the light, unearthly filigree of her footwork in the long duet was remarkable.

As for Baryshnikov's second act, what can one say? There's nothing to compare him to except himself, for his fusion of technical sophistication and expressive intensity is unique and always was. And when he's as thoroughly into a part as he was in this act, the impact beggars description. At one point, after a series of astonishingly elevated leg beats, blindingly swift pirouettes and a double air turn to the knee -- as Albrecht follows Myrta's command to dance himself to self-destruction -- the performance was nearly halted by an understandable ovation. Conductor Connelly sensibly pushed ahead, so as not to break the dramatic tension, but this was indeed dancing for the history books.

There were ancillary pleasures all along the way. Among those that stood out were the dashingly executed Pas de Quatre (formerly the "Peasant Pas de Deux") of the first act, with Cheryl Yeager, Bonnie Moore, Gil Boggs and Johan Renvall as the quartet; Clark Tippet's honest, sturdy and sympathetic Hilarion; and the exceptionally lucid and telling mime sequence by Kathleen Moore as Giselle's mother, Berthe, in which she foretells her daughter's ghostly destiny.

"Giselle" will hold the stage, with changes of cast, through tomorrow night (when Ferri and Baryshnikov will once more be the leads). Thereafter the ABT season will proceed to bring us three more full-length ballets, two world premieres, two Washington premieres, a salute to Antony Tudor and two all-Tchaikovsky evenings, among other goodies.