Elaine Bonazzi is not only an outstanding singer; she is willing to admit a mistake. Saturday afternoon at the Library of Congress, she stopped after the first of David Diamond's "Five e.e. cummings songs for voice and piano" and apologized to the audience: "I would like to do that song over," she said, "because I . . . started on the wrong pitch." The repeat also gave her a chance to correct a small memory lapse, and her interpretation of this witty, bluesy, brilliant, sentimental music was excellent from then on.

Earlier, in Diamond's deeply philosophical cycle "The Midnight Meditation," she had a somewhat larger memory lapse, but this and a momentary imbalance between voice and piano mattered little in the music's total impact. She sang with superbly precise enunciation and phrasing, firm tone and emotional intensity. This cycle, composed for a male voice, has never been performed by a woman before. Bonazzi demonstrated that it can be done effectively by women who sing as intelligently as she does.

The remainder of the program was devoted to three of Diamond's chamber works, which give highly individual harmonic and structural twists to essentially classic (or neobaroque) forms, with particularly effective use of counterpoint in their final movements. This music deserves to be heard more often.

The Clarion String Quartet played well in the Concerto for String Quartet and the Quintet for Piano and String Quartet -- though violist Louise Schulman used a very curious grip on her bow, approximately one-third of the way from the frog to the head. Violinist Robert McDuffie gave a superb account of the brilliant, intensely romantic Sonata No. 2 for violin and piano, which was commissioned five years ago by the Library of Congress. Pianist William Black was impressive throughout the program, in vocal accompaniment and chamber music.