Washington probably has more free concerts of high quality than any other city in this country - certainly more than any city which does not have its own specialized conservatorys like the Curtis in Philadelphia, the Juilliard in New York, the New England Conservatory in Boston or the Peabody in Baltimore. But even among the free riches regularly offered by the Library of Congress, the National Gallery, the Phillips Collection, the Kennedy Center and other sources that appear regularly in our weekly calendar, last week's eighth Inter-American Music Festival was outstanding.

Bringing to various stages in the area three orchestras, two chamber ensembles and a chorus from 'his country as well as a composer-conductor, two pianists, a cellist and a string quartet from Brazil, the festival presented more world and Washington premiers than one might hear otherwise in a while season of concert going.

The last concert I attended in the six-day festival, a chamber program Saturday afternoon in the National Academy of Sciences Auditorium, was typical both in the quality of the performance and the variety and appeal of the music: woodwind quintets by Heitor Villa-Lobos of Brazil and Fabio Gonzalez-Zuleta of Colombia; a brilliant new work by David Amram, a song-cycle by Stephen Burton which combines the sinewy strength of modern music with the more sentimental appeal of the last century, and finally a bright, tuneful march written by Charles Ives when he was a teen-ager. None of the music was familiar to me, and all of it, in its various styles, was worth making a special effort to hear.

The show-stopper f the program was Amram's "Native American Portraits," composed last year for the unusual but very effective combination of violin, piano and precussion and splendidly imaginative in its use of tribal melodies and rhythms for three movements that present musical picture of the Cheyenne, Seneca and Zuni.

The musical forces used in the program ranged from a small chamber orchestra (expertly conducted by Stephen Burton) to a wind quintet to the trio assembled for the Amram work; thus varying the sonic textures continually throughout the program and presenting one more microcosm of the variety that was a hallmark of the whole festival.