Irrepressible energy, great swing, a rhythmic sharpness that can make you jump up and dance, a modern style of melodic invention, an unusually high voice for a blues shouter (and a startling growl, too)--these were LaVern Baker's virtues in the mid-50s. Back then she was among the stars whose rhythm-and-blues shaded into rock-and-roll. Having become famous through a series of novelty hits such as "Tweedle Dee" and "Jim Dandy," she was nonetheless much more than a mere novelty, as her album's worth of Bessie Smith songs accompanied by an all-star jazz band shows. After a long absence from the limelight, she returns this weekend at the Chicago Blues Festival on the same high-powered bill as the clever Jimmy Johnson, the rocking Eddie Clearwater, the unpredictable Clarence "Gatemouth" Brown. The festival's afternoon shows have often been the best, showcasing traditional as well as modern blues. The Front Porch stage, for instance, will offer the fine, rolling piano work of Jimmy Walker, Mississippi-style guitarist Honeyboy Edwards, and the Mississippi Fife & Drum Band on Friday. H-Bomb Ferguson (now there's a blast from the past) will holler at both the Front Porch and Crossroads stages on Saturday; and, as usual, a crowd of top blues artists from Chicago and all over will be on hand. Baker is scheduled to perform at 7 PM Saturday at the Petrillo Music Shell, Columbus and Jackson. The festival runs from 11 Am to sometime after 9 PM today, Saturday, and Sunday on several stages in Grant Park. Call 744-3315 for more.