The subtle virtues of guitarist Akio Sasajima's music resist easy categorization; his choices of tone, texture, and attack are neither radical nor unique. But Sasajima's interpretive and improvisational gifts stem from that selfsame subtlety, manifested in his attention to detail--whether it be the weight of a single note, the overarching shape of a particular solo, or the chordal orchestration he applies to his own carefully considered compositions (which for the last several years have borne his increasingly recognizable stamp). Sasajima has developed into an admirable keeper of the jazz guitar flame passed down from Kenny Burrell to Jim Hall to the younger George Benson, and his music stands above the pack for its clean contours and undeniable authority. He has also become an exciting bandleader, stirring things up with both quicksilver solos and deep-in-the-pocket comping. Now that his estimable strengths are attracting attention elsewhere--particularly San Francisco and his native Japan, where he spends much of his time--local Sasajima sightings have become few and far between, making them all the more worthwhile. Tonight and Saturday, Oz, 2917 N. Sheffield; 975-8100.