MOST JAZZ PIANISTS work from the harmonic architecture of a song, spinning off variations based on the inner logic of chordal voicings or melodic patterns. Ahmad Jamal, by contrast, seems to work best when he unlocks the basic groove behind the song, that essential pulse that explains not simply how a refrain unfolds, but why.

It's a difficult approach to master, especially when the rhythmic treatment usually associated with a song is the wrong one. But when Jamal keys in on the proper approach, watch out -- there isn't another pianist in jazz who can touch him for drive or swing.

"Digital Works," which offers new, digitally recorded versions of the half-dozen tunes for which the pianist is best known, is far and away his most consistent recording yet.

From the bubbling counter-rhythmics packed into "Poinciana" (which he blithely tags with "Hernando's Hideaway") to his thoroughly unsentimental, marvelously swinging version of "Misty," Jamal's simplicity and straightforwardness stand out as cardinal virtues. And his treatment of "But Not for Me" clearly marks what he can do with a melody. Only his new version of "Theme From M*A*S*H" seems overworked, but that's a minor cavil with such a thoroughly listenable album.

AHMAD JAMAL -- "Digital Works" (Atlantic 7 81258- 1-G); appearing Friday and Saturday at Fort Dupont Summer Theater.