Lonnie Shields is one of the Delta region's most popular young bluesmen, a unique guitarist whose stylistic development followed the opposite of the expected pattern: he was a funk player until veteran drummer-guitarist Sam Carr, an alum of Sonny Boy Williamson's aggregation, turned him on to the blues. Since then he's developed a style that's an endearing mix of influences--raw guitar solos that could be straight out of one of the jukes that still populate the countryside around his native West Helena, Arkansas; rough-edged contemporary funk-soul rhythms; brash horn charts that make up in passion what they might lack in finesse. The resulting mixture has won him considerable airplay on black radio stations in the Delta area. But like most Mississippi bluesmen, Shields is best enjoyed live, when his sweaty urgency can keep him going all night. With hot-blooded young men like him carrying the torch, the blues tradition can't be in any danger of dying out in its homeland. Friday and Saturday, 9:30 PM, Rosa's, 3420 W. Armitage; 342-0452.