The Inter-American Music Festival continued at the Kennedy Center last night with the premiere of a work by American composer Leslie Bassett and the debut of an orchestra from the American heartland, the Midland Symphony of Michigan.

If the Midland Symphony, which is directed by Don Jaeger, is symptomatic of the nation's musical health, then the country is doing splendidly indeed. What makes the 82-member ensemble unusual, apart from the fact that its home town has 37,000 people, is the fact that only one-third of its members are professionals. The rest are amateurs, everything from chemists to housewives, a fact belied by their highly creditable performance under Jaeger's sure direction.

Leslie Bassett was on hand to acknowledge the warm applause accorded his Concerto for Two Pianos, which was given an inspired performance by the orchestra and guest artists, Fernando Laires and Nelita True. Bassett has garnered a number of prizes over the years, including the Prix de Rome and the Pulitzer Price, which he won in 1966 for his Variations for Orchestra.

The Concerto for Two Pianos was written in 1976 on a commission from the Midland Center for the Performing Arts. Like other works in Bassett's mature style, it is a work of fascinating and subtle textures which are developed organically. Fragments of sounds beginning in one section of the orchestra would change in shape and color as they were passed from one group of instruments to another. The opening runs in the upper register of the pianios, which were taken up later by the strings, had a particularly haunting quality.

Last night's concert also featured Deems Taylor's engaging orchestral suite, "Through the Looking Glass," based on excerpts from the Lewis Carroll story. Taylor, remembered by many for his writing and radio commemtaries, was an active and successful American composer, particularly during the '20s and '30s. (He had two Metropolitan Opera commissions!) "Through the Looking Glass," written in 1919, was his first success and it remains a work of appealing freshness and honest sentiment, well worth bringing back to life.

Dancer-actress Janet Eilber's interpretation of the Lewis Carroll texts was gifted, graced by wit and sensitivity.

The evening opened with Variaciones Olimpicas, a pleasant, well-crafted work by the Argentinian composer, Robert Morillo.