WORDS AND MUSIC have drawn from each other since the dawn of man. But these days the art of composition has ventured well beyond the simple task of making music out of poetry.

Consider, for example, "The Desert Music" by Steve Reich. Built around several selections from the poetry of William Carlos Williams, it manages, at its best, to brilliantly illuminate the lines.

The second movement finds Williams musing on the nature of music. As the chorus of the Brooklyn Philharmonic observes that the excitement of an orchestral performance descends not from something as simple as the sound of a flute but "the relation / of a flute note / to a drum," Reich's score works out just such a relationship, pulling the thematic elements into breathtaking focus.

Unfortunately, such moments of illumination are all too rare here; for the most part, "The Desert Music" tends to obscure the simple clarity of its text. Part of the problem is the composer's insistence on structural coherence, with the result that the text is too often bullied by the demands of musical development.

More debilitating by far, though, is Reich's weakness for favoring tonal color over content, which turns his vocal lines into incomprehensible sequences of sustained open vowel sounds.

It would almost have been better had Reich resorted to an obscure language, the way Philip Glass does in "Satyagraha." At least with the libretto in Sanskrit, there's less of a likelihood that any listener will complain about diction. But Glass' "Satyagraha," an opera based on the experiences of Mohandas Gandhi in South Africa, goes well beyond simply setting the words to an appropriate set of sounds.

Constance De Jong's text, adapted from the "Bhagavad-Gita," depicts the concept of satyagraha (a combination of the Sanskrit words for "truth" and "firmness") through a slowly unfurled dramatic development that underscores both the gradual process of change and the ethical principles involved.

The music of "Satyagraha" follows the action on a subtly structural level, establishing and unfolding its musical motives with a deliberate lassitude. Essentially, Glass' score demands the sort of attention that would absorb the music at a pace equivalent to the slowly unfolding drama on stage, thereby making the listener's dependence upon the libretto an asset to understanding the piece.

Granted, that's as adamantly post-modern a conceit as contemporary opera presents, but it works well enough to nullify any conceivable complaints.

STEVE REICH -- and musicians, with chorus and members of the Brooklyn Philharmonic, Michael Tillson- Thomas conducting, in "The Desert Music" (Nonesuch Digital 9 79101). Reich will perform "The Desert Music" at the Kennedy Center Concert Hall Friday night.

PHILIP GLASS -- "Satyagraha" (CBS Masterworks Digital I3M 39672).