A WRITER'S REPUTATION sometimes exists in a crazy state of independence, dissociated from the writer himself and sometimes even from his work. It waxes and wanes according to popular taste and critical presence without particular regard to whether the possessor of the reputation may be alive or dead.

Just look at Jack Kerouac. When he exploded forth with On the Road in 1957 (actually his second novel; nobody had noticed his first), he got only a few good reviews but received the sort of popular acclaim that has come to only one or two other American writers in this century: he was the protagonist of the Beat Generation, the avatar of rebellion during the Eisenhower era when rebellion was not quite the thing. By the time it had become the thing in the late '60s, Kerouac had lost his claim to celebrity and was unknown to the thousands and thousands of young people who had, without quite knowing it, followed his lead and gone out on the road in wholesale flight from all forms of authority.

When he died at the age of 47, no more than two or three of his books were still in print, and he was virtually a forgotten man. Since that time, Kerouac's reputation has taken on a life of its own, and he seems to have acquired a literary legitimacy that was always denied him in his lifetime. In the last 10 years there were no fewer than three full-length biographies, all of them at least well-researched and thorough, and all ascribing great importance to him as an author. This year alone we have had Joyce Johnson's excellent Minor Characters, a memoir of Kerouac and the Beat era by a woman who knew him well and remembers him generously; and now comes this critical biography by Gerald Nicosia, Memory Babe, at over 700 pages easily the most comprehensive and detailed of them all.

Everything is included here, in the way of Richard Ellmann's James Joyce and Mark Schorer's Sinclair Lewis. Gerald Nicosia has talked to many, many people who knew Jack Kerouac during the distinct stages of his life, and apparently to everyone still alive who knew him well. The result is a biography that is incomparably more detailed than the three that preceded it. If a man's life is nothing more than the sum total of its moments, then this is as close to an exact re-creation of the life of Jack Kerouac as we are ever likely to get.

Born Jean Louis Kerouac in Lowell, Massachusetts, in 1922, he grew up there as one of the city's sizable French-Canadian minority population. In many ways, his was a typical childhood in an immigrant family. At home the family spoke jual, the patois of the French- Canadians, and he had difficulty with English well into high school. Sports offered him a way out into the great world: he went to Columbia University on an athletic scholarship to play football. In the end, that scholarship did little but provide him with a ticket to New York-- but that was enough, for there, during the war, he met Allen Ginsberg and William S. Burroughs, and the nucleus of the Beat Generation was formed.

Kerouac was, by that time, more or less on his way toward becoming a writer. But spending time with Burroughs and Ginsberg and the semi-criminal set with which they ran, determined not just that he would be a writer, but also that he would be one of a certain kind-- given to exalted, romantic notions of the writer's role, importance, and inspiration; and one who would live and write in an amphetamine fury about those fringe elements of society which many writers of the period were disposed to ignore. But all this came about rather gradually. His first novel, /ka2>The Town and the City, for instance, was fairly ordinary in style and content: an autobiographical treatment of his Lowell and New York experience in the tradition and manner of Thomas Wolfe. It wasn't until he was deeper into the life--or perhaps specifically until he had met Neal Cassady, who to him personified the hipster life--that Kerouac found his true m,etier.

When he did, he fairly exploded into productivity. He tore around the country in pursuit of and in company with Cassady from 1947 to 1950, paused long enough to write the first version of On the Road in 1951, then set off on further peregrinations--to Mexico City, San Francisco, and Denver, usually returning to New York (most often to his mother's) to do his writing. In this way, he did something like seven and a half novels between the writing of On the Road and its publication in September 1957. Afterward, he proved to be not nearly as prolific.

The old story, of course. He couldn't handle success. Although after he was catapulted into stardom, he wrote a couple of good novels (The Dharma Bums and Big Sur), it wasn't long until the problems that had long beset him finally caught up with him. Always a heavy drinker, he was soon deep into alcoholism, from which he managed to rouse himself from time to time to get back to work. The last real job of writing he managed to complete was The Vanity of Duluoz, not at all a bad book, done in fits and starts between 1963 and 1967. That it was finished at all is a tribute to his sense of duty, rather than to his talent or inspiration, for by then he was drinking killing amounts of liquor, eating little, and only fitfully in contact with the day-to-day world. He died an alcoholic death in 1969.

By that time, of course, he was only vaguely remembered as a celebrity from the '50s. Since the publication of On the Road, there could be no talk of Kerouac's critical reputation because he had none. He had become the whipping boy of the literary establishment, reviled as much for his boyish romanticism and predilection for the seamy side of life, as he was for his overnight success. His experiments in speed composition--what he called "spontaneous bop prosody"--especially infuriated some.

That was the '60s, but this is the '80s, and in the intervening decade, Kerouac has not only regained his reading public (he is bought and read today by a whole generation that was not even born when he first emerged so spectacularly), but he is also given the kind of serious critical consideration that was denied him during his career. In fact, when a literary convocation was held last fall in Colorado to celebrate the 25th anniversary of the publication of On the Road, it attracted a great many of Kerouac's fans, young and old, and nearly as many academics who came to read papers discussing various aspects of his work in the usual vocabulary of scholarship.

Each successive biography of Kerouac has seemed to claim more for him. Gerald Nicosia's Memory Babe (its curious title comes from an old Kerouac family nickname), by its very bulk and mass of detail, claims the most. He has given him the great-author treatment here. The fundamental premise is that Jack Kerouac was a writer of such magnitude and importance that even the most mundane happenings in his life, even his drunken mutterings, deserve to be recorded for readers and scholars.

"Great," in fact, is a word Nicosia uses quite often to describe Kerouac's books. In his critical assessments he seems willing to bestow this judgment on many if not most of them. And it seems to have been quite important to Nicosia to get this word out. When the publisher holding the original contract on this book asked him to cut the manuscript by deleting the critical passages, he refused and took it to the present publisher, who agreed to publish the text without such cuts.

Although Memory Babe is disappointing in some ways --it occasionally seems rather awkwardly written, and Nicosia's orientation in jazz and world events of the '40s and '50s is sometimes faulty--his criticisms of Kerouac are actually quite helpful. He has a lot to say about Kerouac's language and syntax that should have been said in the Beat author's defense back in the late '50s and early '60s. But as for meaning and content, there is very little of either in the work that would not be immediately apparent to the general reader. Jack Kerouac was a writer of direct statement. There is not much in his work that needs to be explained by Gerald Nicosia or anybody else.

But was he a "great" writer? Were his books "great" books? Or have critics perhaps recently overcompensated for his previous neglect by claiming too much for him?

Jack Kerouac had genius--no question of it--but in a way, that was all he had, for he lacked a certain fundamental competence in his craft, just as he lacked discipline in his life. All great writers have genius, but not every writer with genius is a great one.