Pianist Katie Webster is legendary among both blues and R & B devotees, having played behind musicians ranging from Louisiana bluesmen Lightnin' Slim and Lazy Lester in the early 60s all the way to Otis Redding from 1966 to his death. For several years she's been concentrating on a solo career, and gigs at such national venues as Antoine's in Texas and last year's Chicago Blues Festival have begun to propel her into the spotlight she deserves. Her piano alternates between thundering boogie and gentle rolling blues melancholy, and she brings the full range of her considerable vocal ability to traditional blues and contemporary pop numbers alike. Katie is also one of the most sophisticated performers of the blues: her stage presence combines earthiness, dignity, and charm with an obvious affection for her audience and a good-time celebratory spirit that is as sincere as it is infectious. Tonight, B.L.U.E.S. Etcetera, 1124 W. Belmont; 525-8989.