Let's face it: At this point, all that really separates Rod Stewart from Michael Bolton are fond memories of the former's first few classic albums. While the nostalgic glow left by his 1993 Unplugged...and Seated is partly redeeming, A Spanner in the Works finds Stewart back on a characteristically muddled course, with songs that range from so-so to awful.
Take ''Muddy, Sam & Otis,'' Stewart's tribute to Messrs. Waters, Cooke, and Redding. Rendering it as a dull MOR ballad, Stewart is blithely unaware of how ridiculously inappropriate synthesized strings sound on a song ostensibly honoring such visceral singers. (A heartfelt version of Cooke's ''Soothe Me'' helps undo some of the damage.) The homespun flavor of Bob Dylan's ''Sweetheart Like You'' is welcome, but what Dylan song wouldn't sound terrific next to such keyboard-choked numbers as ''You're the Star''? You know things are grim when a mediocre rocker like ''Delicious'' is cause for celebration. Still, that marvelous voice remains: raspy, soulful, supple, a natural wonder. What a shame it's not put to better use. C+