Last night's program of the Inter-American Music Festival sandwiched two unfamiliar Latin American works (both enjoying their U.S. premieres) between two works by U.S. composers that were at least slightly more familiar and accessible.

Under the direction of Peter Ero s, the Peabody Symphony Orchestra opened the program with the atonal, colorfully expressive "Avanti" of Gundaris Pone', a work whose spectacular, splashy gestures, high-voltage excitement and fervent, persuasive rhetoric won it the Kennedy Center/Friedheim Award at the beginning of this season.

This was the second time it has been performed by the student ensemble from the Baltimore conservatory, and they had it well in hand, from a percussion-and-brass opening almost as spectacular as that of "Also sprach Zarathustra" through alternating passages of tension and relaxation to a satisfying climax with a slight hint of jazz in its rhythms.

The least serious and perhaps most enjoyable work on the program was Morton Gould's bright, dance-flavored "Latin American" Symphonette, which sent the audience home with something to whistle. The orchestra compensated in vigor and enthusiasm for the final touch of professional polish that it still lacks.

In the Symphony No. 2 of Manuel Enriquez, the most attractive movement was the brilliantly colored Adagio for percussion instruments (including piano and harp used rather percussively). Elsewhere, Enriquez succeeded impressively in producing a lyrical flavor from tightly organized, atonal thematic materials.

The most problematic work of the program was "Aurora," a tone poem for piano and orchestra by Brazilian composer Jose' Almeida Prado, whose fast-moving, varied and colorful "Celestial Maps" for piano solo made a strong impression a few weeks ago at the Library of Congress.

As in that work, Brazilian pianist Caio Pagano was the soloist last night, but this time he had less colorful and dynamic material. In "Aurora," the subject is the end of night and the rising of the sun--a very slow process in Prado's minimalist-flavored treatment. The music seems to hang, static, for long periods, particularly at the beginning when the shades of night still are deep. Later, when the day has begun and birds and animals are stirring about, the music becomes livelier--notably in some birdcall-flavored dialogue between flute and piano. But at the beginning the composer succeeds too well in describing somnolence.

The form seems derived almost entirely from the pictures it is supposed to convey, and the reason for a piano soloist in what seems essentially an orchestral work is not made very clear. Pagano is such a fine performer that any opportunity to hear him should be seized--but on this occasion, he could have been given something more interesting to do.