MIXED MEDIA: <i> A periodic look at pop-related books, videos and laser discs. : </i>

“SEARCHING FOR ROBERT JOHNSON,” by Peter Guralnik. Obelisk/Dutton. $14.95.

In this 83-page volume (basically a long article dressed up as a $15 book), the respected blues author suits up to take on a central Mystery of the faith--but then doesn’t quite do it. Guralnik assembles old and new information to flesh out the brief, shadowy life of the country blues titan, who with just two mid-’30s recording sessions achieved artistic immortality. But the book skirts the puzzle of Johnson’s inexplicably sudden acquisition of his genius (his friends figured he sold his soul to the devil), and Guralnik’s semi-scholarly style lacks the emotional resonance a story about this poet of dread should have. But he does pull off one analogy that neatly summarizes the Johnson enigma: “It is almost as if Elvis Presley had vanished into the Memphis projects under his mother’s maiden name after recording his handful of sides for Sun.”