The sheer variety of contemporary music never ceases to amaze, and often to enthrall, as was evidenced by the 20th Century Consort's presentation last night at the Hirshhorn. With a large and exceedingly attentive audience on hand, the Consort offered works from each of the last three years, along with one from 1928, that encompassed nearly the whole spectrum of modern musical idioms, while containing a common denominator of unusual quality.

James Yannatos' "Songs of Desolation and Joy" (1978) is a brilliant "monodrama" for soprano, using a peculiar assortment of texts, from Dante to Robinson, arranged in such a way as to trace the eternal human conflict between fear and hope. Though such lofty ideas have buried many a contemporary piece in a mass of artificially ponderous music, Yannatos has managed to avoid cliches and to keep the power of his message perfectly delineated through an extraordinary mixture of song and speech. Lucy Shelton reveled in the taxing assignment, turning in the kind of performance for which the term 'tour de force' was invented.

"Luckeystone" (1979), an intriguing duet for pre-recorded tape and clarinet by Timothy Sullivan that also boasts more than a little inventiveness, proved an ideal vehicle for the National Symphony's principal clarinetist, Loren Kitt. The newest work on the program, Richard Wernick's Concerto for Cello and 10 Players (1980), suffers a bit from predictably jagged melodic lines in the first movement, but is redeemed by a vivid, pointilistic tone painting in the second. Barbara Haffner gave a vigorous account of the solo part, and the ensemble, conducted by Christopher Kendall, was first-rate.

The Emerson String Quartet started things off in superb style with Bartok's still vibrant Quartet No. 4.