The Kennedy Center's National Commission on Blacks in the Performing Arts presented two world premieres last night in the Terrace Theater.

Sanford Allen was the violoinist for the evening, with James Gemmell as pianist, in first performances of a Double Concerto Without Orchestra by Roque Cordero of Panama and the Sonata No. 2 by George Walker of the United States. Both Allen and Gemmell are musicians of obvious taste with a flair for new music. In the Mozart sonata that opened the eveining, Allen modulated his tone ideally to suit the character of the writing in which, much of the time, the piano is the dominant voice.

Cordero, whose music has been heard often in Washington during Inter-American Festivals, had the unusual idea of casting his new work in the large mold of a concerto for both violin and piano, giving each its fair share of cadenzas, and creating a symphonic scale in which his strong, sinewy style is very effective.

The work, played as an unbroken whole having four sections, is unified from one major episode to the next through the interlocking of the principal thematic materials.

Altogether it provides serious testing grounds for both instrumentalists. Last night Allen and Gemmell met and matched the composer in impressive fashion. The audience gave both performers and composer a warm response.

The Walker Sonata is much less fortunate. At times, jagged writing in the piano underlines a sustained melody in the violin, a process which is then reversed. On the whole the music is unattractive, whether in the opening declamations, the ensuing perpetual motion, or a finale which starts a bit more appealingly, only to lose its way in inconclusive, nervous bursts. The audience was quite clear in its lack of enthusiasm for the piece.