The president of the New York unit of the American Federation of Musicians was arrested Saturday night in the lobby of the RCA building in Rockefeller Center after he entered the building to lead a protest against a non-union orchestra playing in The Rainbow Room, a nightclub on the 65th floor.

John Glasel, the newly elected head of the musicians' Local 802--one of the largest entertainment unions in the nation--said he intended to put an end to what he alleged was widespread payment of substandard wages to musicians here and to the use of taped music at live ballet and opera performances.

Glasel and another union member were charged with criminal trespass.

Some 20 other union protesters moved off of Rockefeller Center property and were not arrested. Glasel was later released by police and ordered to appear in court at a future date.

Union officials charged Saturday that Rockefeller Center had abridged their right of free speech and that they would return Sunday night to resume informational picketing. Their labor dispute, they said, is not with Rockefeller Center, which does not run the nightclub; but they said to call attention to their grievance, they must protest within the huge Rockefeller Center complex. Rockefeller Center maintained that the musicians should picket on public streets and not on private property.

The union members said they were prepared to be arrested at the picketing scheduled for Sunday night.