MOST JAZZ composers write at the piano, even if their onstage instrument is something else, so it's not surprising that fulltime pianists have often been the best composers of their times. Some of the best jazz composers of our era are pianists, and these are their latest albums:

THE SUN RA ARKESTRA -- "Reflections in Blue" (Black Saint BSB 0101).

Sun Ra may be one of the most gifted and underappreciated figures in jazz history, but he has done little over the years to make his eccentric, dissonant records accessible to the general public. That's why this album is such a breakthrough, for it isolates the swing and melody at the root of all his music and presents it in one undiluted dose. Sun Ra's own tunes have as much body as the two by Jerome Kern, and he disassembles and reassembles them with the idiosyncratic imagination of a Thelonious Monk. His longtime, unparalleled reed section blows one inspired solo after another.

THE DON PULLEN-GEORGE ADAMS QUARTET -- "Song Everlasting" (Blue Note BLJ-46907).

Pianist Pullen, saxophonist Adams and drummer Dannie Richmond all played with Charles Mingus, and Mingus' combination of bluesy passion, churchly spirituality and Ellingtonian technique is unmistakable on this disc. Eight years of playing together have given the quartet a rare unity, and both Adams and Pullen compose boldly emotional musical statements that Mingus would have been proud of. Pullen's 10-minute, hymn-like title tune is a future standard that has already received its definitive treatment.

JOANNE BRACKEEN -- "Fi-Fi Goes to Heaven" (Concord Jazz CJ-316).

This is Brackeen's first record as the leader of a quintet, and the presence of saxophonist Branford Marsalis and trumpeter Terence Blanchard emphasize the vocal quality of the pianist's writing and playing. Brackeen has a way of caressing the keys firmly that rounds off her phrases and gives them the emotional and lyrical quality of the human voice. The patient, full-toned solos of the horn players and Cecil McBee's melodic bass lines amplify the implications of Brackeen's four originals and her arrangements of three standards.

THE ANDREW HILL TRIO & QUARTET -- "Shades" (Soul Note SN 1113).

Without much recognition or reward, Chicago pianist Andrew Hill has been making high-quality albums since the early '60s. He begins his newest effort, recorded in Europe where he has most often worked lately, with "Monk's Glimpse," and the rest of the record reflects the spare, angular approach of Thelonious Monk. The demanding rhythmic punctuation and melodic ellipses of Hill's writing are handled with assurance by Chicago saxophonist Clifford Jordan and Monk's former drummer, Ben Riley.

ELIANE ELIAS -- "Illusions" (Blue Note BLJ-46994).

This 26-year-old Brazilian pianist is best known for her stint with Steps Ahead, the American fusion band, but her debut solo album finds her leading three different acoustic piano trios. She gets all-star help from the likes of Steve Gadd, Al Foster, Eddie Gomez and Stanley Clarke, but she dominates the record with her fleet fluid piano runs which remind one of Bill Evans and the acoustic Chick Corea. She's at her best on her three originals, but she still lacks the darker moods and dramatic tension that might anchor her facility and lyricism.