Minimalism, detractors would argue, is music stuck in a rut -- like a phonograph needle in a record -- weighted down by its own lack of invention. For these critics, works by composers such as Philip Glass, Steve Reich and Terry Riley resemble interminable tape loops, on which the music goes 'round and 'round and 'round, mesmerizing the listener into responsive nods -- not of approval, but of impending slumber.

There's no denying that repetitious melody and rhythm can induce a certain hypnotic state and that the minimalist's art has on occasion "nuanced" audiences to distraction, if not dreamland. On the other hand, well-organized pieces that fluctuate between predictability and surprise have the ability to bring one -- fully conscious -- into the composer's realm. Such is the case in two recent compact-disc recordings by Reich and Riley, pioneers of minimalist "phase" and "pulse" music since the '60s.

Reich's "The Desert Music" (Nonesuch Digital 79101-2; -1F, LP; -4F, cassette) lasts nearly 50 minutes and is scored for an orchestra of 89 and a chorus of 27, forces considerably larger than his chamber ensemble, which performed the work at the Kennedy Center Concert Hall Friday night. The title, named for a poetry collection by William Carlos Williams, is a bit misleading because the texts have nothing to do with deserts per se. Instead, Reich uses Williams' verse metaphorically to suggest a desolate setting where mankind tries to sort reality from hallucination and to comment on his survival prospects for the future. Strings, brass, winds, percussion, synthesizers and voices, which open and close the symphony with a wordless, vibrant chorale, establish mood.

The five-movement design is tightly knit, with repeated harmonic cycles of pulsing chords and texts providing continuity. The slow movement, within the larger framework, functions as the keystone, for it is the longest section and receives the most lavish percussion treatment. Here Reich manages to mix a bit of irony with his cosmic overview. When the chorus sings "It is a principle of mine to repeat the theme/ Repeat and repeat again, as the pace mounts," syncopated for dramatic emphasis, it also is espousing the composer's philosophy.

Conductor Michael Tilson Thomas leads members of the Brooklyn Philharmonic, musicians from Reich's own ensemble and the chorus in an emotionally charged performance that receives an extra boost from Nonesuch's digital clarity. With no pauses between movements, transitions are abrupt; yet Thomas makes smooth connections without so much as ruffling a bar line. He clearly draws out the interlocking rhythms, most noticeably in the strings and mallet percussion instruments, which constantly reinforce the pulse.

"The Desert Music," Reich's most ambitious piece to date, is a culmination of his career. The complex rhythmic patterns found in an earlier work, "Drumming," the form and pulsing chords from "Music for 18 Musicians" (now available on CD -- ECM 1129-2) and the thick-textured canons of "Tehillim" all coalesce in this symphony. Reich has achieved the enviable goal of retaining his judicious approach to rhythm and melody and infusing it with a profound expressive power that just might win over the opposition.

No less persuasive, though a great deal more surprising, given his modus operandi, is Terry Riley's collection, "Cadenza on the Night Plain" (Gramavision 18-7014-2; -1, 2 LPs; -4, cassette), featuring the Kronos Quartet, a feisty and youthful San Francisco-based group that now devotes its repertoire exclusively to 20th-century works.

Riley, whose "In C" sent minimalism on its merry way in 1964, seems an unlikely quartet candidate. His background is rooted in jazz and Indian Classical music. Furthermore, he's shown an aversion to writing for ensembles; he prefers to compose and perform live as a one-man band. He does this by improvising melodies on electronic keyboards, backed by a series of tape recorders using delayed playback, which enables him to devise aural collages with overlapping rhythmic webs that spiral, loop-the-loop fashion, as he slowly alters the stress. In short, Riley loves ambiguity.

He and the Kronos, however, have a least one thing in common: Mills College, in Oakland, where Riley taught and the players were in residence. Their affiliation, based on the recorded evidence, has been mutually profitable. Riley's whimsical nature, low-key manner and concern for quality rather than intensity of sound complement the Kronos' fiery virtuosity and impetuous feel for contemporary music.

One need go no farther than "Sunrise of the Planetary Dream Collector" to hear how well they work together. Using the composer's suggestions, the musicians select from a series of written 14-beat phrases and build from there. "Sunrise," therefore, is different each time out. Consistent elements include a rhythmic intensity reminiscent of Barto'k and modal melodies suggesting Debussy and Ravel.

"Mythic Birds Waltz" is a mystical wedding of raga and ragtime, of Indian rhythms and Baroque 16th-note sequences a la Corelli. The dazzling strings imitate sitars, interject drones and swing the beat when not pouring forth spacious sustained chords. It's a quixotic combination, Riley explains in the notes, "that makes sense in retrospect."

The same applies to "Cadenza on a Night Plain," a wide-open musical terrain that embraces, to name just two, the American Indian and a division of over-the-hill hippies, perhaps trudging off to defend our nation against varmint weed-eaters. During the course of 13 sections, punctuated by a cadenza each per quartet member, Riley waxes pictorial, folksy, spiritual. Unusual string tunings add color to his more impassioned statements. When the Kronos dig into "The Night Cry of Black Buffalo Women," the wail becomes a cry for all humanity.

The only flaw with this CD is the mistiming and inadequate indexing of "Cadenza," but the CD's sonic presence far surpasses the cassette version, with one major compromise: The cassette (and LP set) have an extra track, "G Song," that couldn't fit on the CD, generously filled with more than 63 minutes of music.

Reich and Riley make an awfully strong case for minimalist art. The chorus in "The Desert Music" asks, "Well, shall we think or listen? Is there a sound addressed not wholly to the ear? . . ." To appreciate these composers' works, no choice is necessary: Thinking and listening go hand in hand. As for the second, it's a rhetorical question.a Washington writer and editor.