THE DE-MYTHING of Jack Kerouac continues; a poignant, major American spirit is now beginning to assume his full stature in our distracted national consciousness, 10 years after his death. This is the third full-sized Kerouac biography for the general reader to appear in the last six years. It is a testament to the fascination of his story, with all of its cultural reverberations, that none of them quite repeats another. And as sure as we're Americans living through characteristic wild times, other studies are certain to follow.

Ann Charters broke the ice -- and the media stereotype of the cockeyed, brazen "king of the beats" -- with her pioneering Kerouac in 1973. Barry Gifford and Lawrence Lee surfaced with their crisp "oral biography," Jack's Book, last year. Now comes Dennis McNally, using the disciplines of a historian to trace Kerouac's meteoric flight from a New England mill town to all the corners of the contemporary world. Like the black jazz musicians he most identified with, it was Kerouac's inevitable fate to be recognized abroad with more dignity and respect than he ever was shown at home. Death, however, has indeed brought him home to stay; as is so often the case with us, once the pure spirit has been separated from the disturbing flesh we rush to do penance.

McNally makes it plain, cooly, objectively, that there was much about Kerouac that could not fit into our preconceived categories. The ridicule that he received from our most self-assured culture-clockers -- Time, Mike Wallace, Saturday Review, Partisan Review, etc. -- was almost preordained. How could the average Establishment critic make sense of this son of a French-Canadian, working-class, righteously Catholic family fathering something called the "Beat Generation," with all its seeming blasphemies and nose-thumbing at assumed American values? More, how could hard-boiled media pulse-takers drop their suspicions before novels that were written in "spontaneous bop prosody," a prose that approximated a nonstop jazz solo and in which it was a sin to rewrite the mistakes that "God's hand" had committed in the first draft?In retrospect, it was too much to hope for.

The chief value of Dennis McNally's doggedly researched biography is that he brings all these seeming anomalies into the light of clear, tangible sense. The secret thread is in understanding the contradictions of Kerouac's personality and influences.

Born in Lowell, Massachusetts, on March 12, 1922, it might have been predicted that Jean Louis Lebris de Kerouac would follow his post-immigrant boyhood friends into the mills of northern Massachusetts. But in spite of his tribal loyalty to being "just one of the boys -- something he was to return to before he died, having become totally saddened with his role as half-freak, half-celebrity -- Kerouac was set apart by two compelling drives: an ever-rich fantasy life that alternately frightened and thrilled him, and a desperate need for absolution after the sudden death (by rheumatic fever) of his nine-year-old brother, Gerard, in 1926.

All his adult life, as McNajly shows, Kerouac's tough and accusing mother held him responsible for the death of the young "saint" Gerard; this bond of guilt lasted throughout Kerouac's 47 tormented years, even though it was well disguised by his clean-cut, all-American looks, jock prowess (a football scholarship took him to Columbia) and Jack London roustabouting. The need for explanation -- his refusal to kill so much as a cockroach, let alone defend himself in drunken brawls -- led him past Catholicism to Buddhism and finally to his own brand of all-embracing mysticism. And his compassion for the "holy" deviants of his generation permitted him to learn from an unprecedented spectrum of sources, ranging form the poetic hot-rodder Neal Cassady (Dean Moriarity of On the Road) to such homosexual visionaries as Allen Ginsberg and William Burroughs.

Add to this the fevered restlessness of America after World War II, and you get some idea of what an authentic lightning rod Kerouac became for unacknowledged new forces of energy whirling through the underground of the Eisenhower years. It could only have taken a unique combination of history and personal needs to draw all this together, as Dennis McNally makes clear, the tragedy of the Kerouac story is that it could only be sustained to a certain point.

By the time he was 40, Jack Kerouac's major writing was behind him. Notoriety shattered his fragile balance. He and his mother, locked in one of the most curious oedipal situations in modern American lit, were both heavy drinkers; he became an alcoholic and finally died of a massive stomach hemorrhage on October 21, 1969, in St. Petersburg, Florida. The man on the operating table was already a ghost who had outlived and disowned his own beat Beat Generation.

Like all the Kerouac biographers thus far, Dennis McNally loves his martyred subject to the point that his own professionalism occasionally deserts him: "There was only one god Jack could really worship, and it was inside a typewriter." But these pulp-magazine lapses are comparatively unimportant. We are only beginning to catch up with an extraordinary life that was loved and expressed in our largely uncomprehending midst, and McNally's narrative is probably the most riveting to date.