Mikhail Baryshnikov will dance the role of Prince Siegfried in "Swan Lake" -- for the first time in the United States -- in Sunday evening's ABT performance at the Kennedy Center Opera House, American Ballet Theatre announced yesterday.Although a performance of this ballet had been previously scheduled, no principal casting had been announced until last night. Baryshnikov will, moreover, be dancing in the celebrated ballet classic for the first time anywhere opposite Natalia Makarova as Odette-Odile.

ABT begins a three-week engagement at the Kennedy Center tonight, with a gala opening program in which Baryshnikov will be dancing in "Bournonville Pas de Trois," partnering Cynthia Harvey and Susan Jaffe," with its familiar Tchaikovsky score, are scheduled for the run.

Baryshnikov, who became director of ABT last September, never danced a full-length "Swan Lake" while he was in Russia. A year after his defection to the West in 1974, he appeared as Siegfried in full-length "Swan Lake" productions both with the National Ballet of Canada and England's Royal Ballet. On several occasions since then, he has expressed reservations about dancing the role of Siegfried, mainly because of his dissatisfaction with traditional productions of the ballet. In an interview last fall, he said he planned eventually to completely restage the ABT version (the current repertory production, by David Blair, dates back to 1967), and said also he hoped to induce film director Franco Zefirelli -- who had expressed interest in the projects -- to undertake new decor. As a first step toward such revision, the "Swan Lake" performances now to be seen at the Kennedy Center will include some minor choreographic retouching.

Makarova, who is one of the most admired contemporary interpreters of the dual Odette-Odile role, was Baryshnikov's first partner in this country, in the ballet "Biselle."

A number of changes in casting for the week of performances were also announced by ABT yesterday. Principals in the Saturday matinee performance of "Swan Lake" will now be Magali Messac and Victor Barbee; and for the Sunday madtinee performance of the same ballet, Cynthia Harvey and Kevin McKenzie. In tomorrow evening's program, the cast for "Airs" will be the same as in tonight's performance, and the principals in "Theme and Variations" will be Cynthia Harvey and Ronald Perry.