Mikhail Baryshnikov did his best dancing of recent seasons in "Push Comes to Shove" here on Saturday afternoon. One second he was standing at ease, the next he was turning corkscrews in the air or sliding to a goal-post finish. He'd already danced the whimsical male lead in Twyla Tharp's quirky opus on the opening night of American Ballet Theater's current run at Kennedy Center, but not like this. The dynamics were incredible, the scale spectacular and there was not the slightest sign of that strain at the base of the neck that first surfaced during the strenuous rehearsals for his "Don Quixote" a couple of years ago.

ABT's notorious caste system was already being shaken up last spring when corps dancers suddenly began appearing in principal parts. Baryshnikov's regime is consolidating that policy. At both Saturday performances soloists were seen in some minor roles, corps dancers in some major ones, productions looked rather rehearsed, and intermission-time seers declared that they detected a new spirit of disciplined daring.

Two of the female leads in the "Push" were newly tackled by dancers from the ranks. Elaine Kudo made the miniflapper in orange look wacky, and Pamela Nearhoof was an Ann Sheridan type with her sultriness matter-of-fact. Technically, neither had cause to be ashamed of dancing with their director. This performance almost made Tharp's revised exploitation of Haydn's 82nd bearable.

Nearhoof also was a new Cowgirl in de Mille's "Rodeo." To make up for being too pretty for the ugly duckling part, she became flagrantly mannish. Robert La Fosse, her winning Roper, continued to surprise with his young hero characterizations. He caught the innocence and knowledge of a 1940s American in Robbins' "Interplay," though letting the dancing flag this time.

There were newcomers for the Russian repertory, too. Chrisa Keramidas, of the fine long Taglioni arms, danced the waltz in the afternoon's "Les Sylphides" with a smoother Cynthia Harvey, a still-too-sweet Cheryl Yeager and a more expansive Baryshnikov than in last Thursday's cast. At night, Kevin McKenzie, a touch too dry for Baryshnikov's re-romanticized staging of this Fokine classic, escorted the anonymous Lisa Rinehart, an almost disciplined Hilda Morales and a Marianna Tcherkassky, who danced brilliantly.

New stylishness by the familiar cast, long-legged Susan Jaffe (minus the sack-cloth veil) and monumental Alexander Godunov, was shown in the afternoon's archeological artifact "Pas d'Esclave." George de la Pena, of "Nijinsky" film demifame, made his ABT reappearance in a minor role in the evening "Raymonda." He looked like a star, but didn't dance like one.

It takes no seer to see how important matters of look and manner have become in ABT. The formaility of the Old-Russian works is projected, and so is the casual air of American pieces; Old-American, like "Interplay" and "Rodeo," is given a direct delivery while the recent "Push" is danced for all its wiles.