Woody Guthrie, the patron saint of American folk music, died in 1967, but his life had slipped into near mythology long before. The Okie fudged facts in his autobiography ''Bound for Glory'' and feigned an accent as an unschooled hick to disguise his middle-class roots. Cray examines Guthrie more as a political activist than a musician, often getting bogged down in extraneous detail. But he also conjures a vivid portrait of an anxious man, haunted both by family tragedy and the FBI, who charmed everyone despite a host of repulsive habits (slovenliness, serial infidelity, petty thievery). He was ''a talented bum without any morals or scruples,'' says one acquaintance, and one suspects it's true.