POSTHUMOUS releases are common in the record industry, but the material generally falls into two categories: flawed or incomplete takes never intended for release; or insignificant material which adds little, if anything, of value to the musician's reputation or discography.

The problem is particularly acute in pop music. The lucrative Jimi Hendrix and Elvis Presley catalogues are choked with false takes, ephemera and afterthoughts. In jazz the problem is less severe if only because a new generation of fans is discovering seminal jazz artists for the first time; thus reissued recordings tend to dominate older collections. Rarely does a new recording, much less a collection, come along that provides a fresh perspective of a musician long dead. Yet it's hard to imagine a future jazz discography that won't reserve space for the "Prez: Volumes I-III" (Pablo 2308-219, 225, 228).

Like the first two records, the recently third volume captures the wispy, soft-spoken Lester Young swinging with imperturbable ease at Olivia Davis' Patio Lounge here in Washington in 1956, Backed by a young, eager rhythm section -- bassist Norman Williams, drummer Jim Lucht and pianist Bill Potts (who had the foresight and good fortune to produce and preserve these tapes) -- Young's tenor saxophone effortlessly unfolds several tunes he previously had recorded, including two -- "Sometimes I'm Happy" and "There Will Never Be Another You" -- which largely became jazz standards thanks to his singular talent.

As its title suggests, "Sometimes I'm Happy" is a fitting example of the saxophonist's reflective yet almost inspirational music. Young always prided himself on knowing the lyrics of the tunes he played; his delicate placement of notes and graceful choruses were always mindful of the lyric even when, as on this piece, his phrasing grew more assertive with every passing bar.

Young always maintained an elegant sense of economy; moreover, his tenure with the Count Basie Band left him with a lasting appreciation of uncluttered accompaniment, something particularly evident on the "Prez Volumes," where the functional rhythm section never intrudes on his many alluring, vulnerable choruses.

The selection of tunes also displays Young's gifts handsomely. His own "Up N Adam" and "Gs If You Please" are given aggressive yet undeniably graceful readings. "Indiana" retains much of its cheerleader charm with Young in full command, just as he was four years earlier recording the same tune with a decidedly different group featuring Oscar Peterson and Barney Kessel.

A fourth volume is expected to complete this impressive collection of Young's later work; all of it has been restored to surprisingly good audio quality by engineer Jack Towers. Incidentally, Pablo doesn't have a monopoly on rare and important sessions by Young. Lester Young's "Master Takes" with Earle Warren and Johnny Guarnieri (Savoy SJL 1133) and "Lester Young and Charlie Christian" (Jazz Archives-JA 42) are both recent and revealing additions to his discography.

Another saxophonist, Washington's Buck Hill, has a new album out, though it's been available in Europe for some time. Hill's first album on the Danish Steeplechase label received exceptionally favorable reviews and his latest, "Scope" (Steeplechase SCS 1123), deserves an even stronger response. Hill has written all of the tunes -- fresh, imaginative, vigorous pieces strongly supported by a powerful rhythm section comprised of pianist Kenny Barron, bassist Buster Williams and drummer Billy Hart.

Hill sets the tone for the album immeidately on the title track, positioning his aggressive sax against the chattering cross-rhythms traded between Williams and Hart. Slowly, almost cautiously, Barron enters the fray filling in the spaces left behind by Hill's searing, circuitous lines. On the moody "Ballad Repeter," cast in the shade of Hill's arching figures, Barron and Williams' spacious romanticism and Harths shimmering accents, the musicians again come together as one.

"Little Bossa," a breezy interlude, boasts the album's most memorable melody, while "The Sad Ones" evokes Ben Webster's breathy lyricism on more than one occasion. Ultimately, however, it is Hill's own formidable breath control that impresses the listener most. His performance of ballads is warm and expressive, but it frequently pales in comparison to the explosive, demanding excursions he favors. Hill's at his best in high gear, hurdling across the changes on "Beast Beautiful" or challenging his rhythm section on the title track. Few musicians in jazz possess his muscle and drive.

Finally, Plunky and Oneness of Ju Ju, an ensemble based in Richmond, Va., that appears frequently in the Washington area, has issued an album (produced locally) titled "Make a Change" (Black Fire-BF 19811). Plunky refers to Plunky Nkabinde, a multi-talented musician whose contributions on reeds, percussion and vocals are largely responsible for the band's textured sound.

Under his direction, the group frequently combines positive, inspirational lyrics with bright, if not particularly distinctive, melodies. Too often his broad synthesis of styles, in which jazz, rock, soul, reggae and gospel elements commingle, lacks an identity of its own.

Since the funkathon "Every Way But Loose" and the gospel-inspired "Higher" are obviously tailored for a live audience, they seem overly long on record. The reggae beat on the title track proves more durable, but again the band has to make up in energy what it lacks in imagination. Fortunately, it has energy and talent to spare. The group numbers more than a dozen musicians and most of them -- particularly the unidentified female singer whose soaring vocal on "Always Have to Say Goodbye" is the highlight of the album -- deserve more distinctive and challenging material.