From the time of Copland's first visit to Mexico City in 1932, when his friend Carlos Chávez took him out a nightclub called ''El Salón México'', Copland wanted to compose a piece about the unusual dance hall. He said, ''I was attracted by the spirit of the place and by the Mexican people. Using Mexican melodies seemed appropriate. My purpose was not merely to quote literally, but to heighten without in any way falsifying the natural simplicity of Mexican tunes.'' Much to Copland's surprise and delight, ''El Salón México''was welcomed warmly in Mexico and has consistently been one of his most performed pieces. He said, ''Never in my wildest dreams did I expect the kind of acceptance for the piece!''