UNFORTUNATELY it sometimes takes a death to force us to recognize a musician's greatness. Since Thelonious Sphere Monk's death last Feb. 17, more and more people are admitting that the eccentric pianist rivals Duke Ellington as jazz's most important composer. In fact, it's been difficult to attend a jazz show this year without hearing at least one Monk tune. Nevertheless, no one has played those compositions better than Monk himself, and his death has sent record companies scurrying to their vaults to dig out unreleased tapes.

The digging has thus far yielded two double live albums and a double album of alternate takes. Though these four albums contain quite familiar titles, they reaffirm Monk's brilliance as an improviser. Every performance was an act of recomposing the song; thus every performance is worth hearing. The next best thing to hearing Monk himself is hearing the musicians who worked closely with him applying their rare education to his compositions. Two Monk alumni are at the core of Sphere, and this new quartet's debut album is the best ever record of Monk music without Monk.

The most revealing of these posthumous releases is Thelonious Monk and Gerry Mulligan's " 'Round Midnight" (Milestone, M-47067). The first three sides include the six numbers from the 1957 Riverside album, "Mulligan Meets Monk," plus four alternate takes from those sessions. It's a fascinating encounter as the leading voice of the West Coast "cool jazz" movement wades into the tricky waters of Monk's music. On the alternate takes, one can hear Mulligan getting his feet wet and then adjusting to the stiff current.

He adapts quickly, and his low, fat baritone sax is a revealing contrast to the tenor sax usually found in Monk quartets. The baritone adds a new, elegant depth to " 'Round Midnight." Side three contains three takes of "I Mean You," and one can hear Monk's piano phrases educating Mulligan on the purpose of pauses. Unlike most alternative takes, these grow slower and sparser until Mulligan strips down his playing to concentrated, Monk-like phrases.

What makes this album a must for Monk enthusiasts, however, is the fourth side. The famous six-minute solo piano version of " 'Round Midnight" on the 1957 album, "Thelonious Himself," was preceded in the studio by 22 minutes of trial-and-error improvisation and refinement. The entire half-hour survived on tape and is available here. Monk stops himself with comments like, "I can't hear that," and then reapplies himself with renewed effort. " 'Round Midnight" is Monk's most famous tune because it combines a melody as pleasurable as romance and a rhythm as tense as romance. As he works on the piece, he uses our longing for that melody to wind the tension tighter and tighter until the final take is almost unbearable.

The two live albums capture the same quartet playing much the same repertoire five days apart. The quartet is Monk, tenor saxophonist Charlie Rouse, bassist Larry Gales and drummer Ben Riley. "Live at the It Club" (Columbia, C2 38030) was recorded in Los Angeles Oct. 31, 1964; "Live at the Jazz Workshop" was recorded in San Francisco Nov. 4. The L.A. date boasts brighter sound and especially good nights by Rouse (whose tone has seldom been fuller) and Riley (who has seldom been as aggressive). Monk's playing on the date is sharp and jagged, as he frames his piercing chords with unpredictable pauses. The Frisco date features a less predictable repertoire and finds Monk in a more playful and exploratory mood. It contains two austere, thoughtful piano solos that segue effortlessly into hard-charging ensemble pieces. It also contains a humorous treatment of the standard "I'm Getting Sentimental Over You" and an expanded treatment of Monk's lesser known composition "Bright Mississippi."

Rouse and Riley joined two of New York's most underrated musicians--pianist Kenny Barron and bassist Buster Williams--to form Sphere this year. The quartet recorded its debut album of six Monk tunes, "Four in One" (Elektra/Musician, 9 60166-1), on Feb. 17, but did not know until they had finished that Monk had died that morning. Rather than recycle Monk's most familiar titles, Sphere has chosen to spotlight some of his lesser known gems. Each tune bears the unmistakable Monk imprint of strong melodies in pause-broken phrases. The title tune's melodic figure is restated continually in sharp, stabbing thrusts, each from a slightly different angle. Even more revealing are the two ballads -- "Light Blue" and "Reflections" -- which seem to proceed reluctantly, as if wanting to savor each unexpected harmony.

Kenny Barron faces the unenviable task of filling Monk's piano chair. Rather than imitate the composer's unorthodox, angular style, Barron transforms the pieces into his own intelligent, fluid style. This gives a new feel to the tunes, especially the ballads. Rouse is not an all-star saxophonist, but he has been thoroughly immersed in the Monk style and plays it more intuitively than anyone else. The real star of the Sphere album, though, is Buster Williams, whose big, round notes and sliding harmonies bring out the bottom of Monk's music as never before.

These recordings show how many shapes the same Monk composition can take. On "Four in One," Sphere gives "Evidence" a sinuous continuity that makes the piano melody line and the bass harmony line more evident and more attractive. On "Live at the It Club," Monk gives "Evidence" one of its most angular readings as he drives the altered chords like sharp spikes into the piece. On "Live at the Jazz Workshop," he uses arpeggios to transform the chord progression of "Evidence." He gradually modulates the chords into those for "Rhythm-a-ning"; his startled band catches on and jumps on the new tune for a lively exit.

On "Live at the It Club," "Rhythm-a-ning" is pushed into a breathless tempo by Riley's drum rolls and Gales' jogging bass lines, but Monk refuses to be hurried as he toys with the melody by playing below it and above it. On " 'Round Midnight," Monk pushes Mulligan on "Rhythm-a-ning" to play higher and faster than baritone saxophonists are used to. Mulligan makes good use of his expanded options. Monk's own solo is a bravura display of fast triplet blazing nonchalantly through his chord alterations.