TWO NEW RELEASES by the Modern Jazz Quartet span the years since the group reunited in 1981. The first, "Reunion at Budokan," documents two 1981 concerts in Japan, where the quartet "first reemerged after a seven-year hiatus. The second, "Topsy," is a new Count Basie- inspired studio session, featuring several familiar pieces in fresh settings, and something new as well.

Whether working with MJQ or in his own band, vibist Milt Jackson can always be counted on to swing effortlessly in concert, and the Budokan recording offers plenty of room for his deft improvisations, especially on his own tunes. "The Cylinder," "Really True Blues" and the inevitable encore of "Bags Groove" have an easy yet compelling momentum, and Jackson's bluesy expressiveness infects the playing of pianist John Lewis, bassist Percy Heath and drummer Konnie Kay.

Even "Odds Against Tommorrow," an otherwise rather dainty slice of impressionistic film music written by Lewis, comes alive once Jackson is free to roam. Lewis' "Jasmine Tree," an exotic and tightly integrated ensemble piece, has to rank as the album's remaining highlight.

Jackson also has his moments on the album "Topsy," beginning with his own "Reunion Blues," which sports a bright and harmonically rich new arrangement by Lewis. A lovely and ultimately stirring solo treatment of "Nature Boy," now a staple of Jackson's concert performances, is also included.

But it's Lewis who plays the dominant role on this recording. He salutes Basie directly with ease and economy on the title tune, and indirectly with similar results on an old MJQ tune called "D and E" (which turns out to be a fine showcase for Heath as well). What's more, Lewis caps the album by taking the opening six notes of the Miles Davis tune "Milestones" and creating an alluring new piece called "Le Cannet."

THE MODERN JAZZ QUARTET -- "Reunion at Budokan" (Pablo Live D 2308-243); "Topsy" (Pablo 2310-917). The Milt Jackson Quartet appears at Blues Alley Friday through Sunday.