Rockettes meet the Vienna Choir Boys;

It's Spring "Holiday spectacular" conceived and produced by Robert F. Jani. Musical director, Donald Pippin. Directed and choreographed by Dru Davis and Howard Parker with Violet Holmes for the Rockettes).

"The Rockettes think your singing is exquisite," chorus the New Yorkers to the Vienna Choir Boys in the finale of the latest extravaganza at the Radio City Music Hall Entertainment Center. To which the golden- voiced youngsters reply: "The Rockettes are the reason for our visit."

It's a mutually graceful summing up of the meeting of two worlds in the 90 -minute, six- part spectacular, "It's Spring," which will be filling the great house with the sound of music and other diversions through April 13.In keeping with the institution's new era, the show is opulent, smartly performed, and varied enough to suit the family audiences the management seeks to please.

"It's Spring" begins with a variant of the traditional Music Hall standby, "The Glory of Easter." The principal variant in this case is the presence of the Vienna Choir Boys, who launch the program with their unique ensemble singing in the "Haec Dies" of Jacobus Gallus, Franz Schubert's setting of "The Twenty Third Psalm," and Anton Rubinstein's florid "Kamenoi Ostrow." As the music swells, the singers are joined by a pageant-like procession of stage folk garbed in Music Hall medieval costumes featuring long trains and towering head pieces.

From this ornate and grandiose introduction, "It's Spring" segues into a secular mood. As the orchestra surfaces enclosed in a pit-wide gazebo, the cheerful New Yorkers break into Irving Berlin's "Easter Parade." Comes then the Rockettes' first appearance. Clad in white tights and tails, Kelly green vests and green-tinted toppers, these incomparable precision dancers achieve their high- kicking purpose by bringing down the house. There is a magic section in which not one, but four, lovely New Yorkers are made to disappear and reappear in those magic boxes. And there is a suitably fantastic version of Walt Disney's "The Sorcerer's Apprentice" by the famous People Players), a black-light puppet troupe from Toronto. The sailor-suited Vienna Choir Boys return for a medley of folk songs, and the whole celebration ends in an aura of reciprocal bilingual admiration which embraces the audience in its springtime spirit of good cheer and optimism.