Alcatraz is not a penitentiary. Alcatraz is Alcatraz,"" an early warden of The Rock told each incoming prisoner. He meant that Alcatraz was the Federal penal system's black hole for ""incorrigible incorrigibles""-- the worst possible prisoners. (Or it was until last month, when Attorney General Robert Kennedy closed it down as prohibitively expensive to repair.) Alcatraz was also the repository for the nation's most ingenious escape artists, and this book is a close history of each of those who tried practising his art on the fabled, escape-proof island. The escapees average out at one for each of The Island's thirty years, though the breaks were made in small, intimate groups. Through ingenuity and incredible resourcefulness, the convicts urrowed, scraped, climbed and blazed their personal escape routes out of the prison proper, only to meet disaster at shore's edge or in San Francisco Bay's 0 water and heavy tides. Many escaped simply into their own winding sheets. Others swam out a ways, groaned and returned (one frozen man climbing right back into prison in the way he'd come out.) Two on a driftwood raft were certainly swept out to sea, presumably, as well as three others. One man alone did swim the three-mile channel, only to arrive under Golden Gate Bridge too beaten to continue. Yet--a girl in her teens once swam out to The Rock in 47 minutes, while another circled it and paddled blithely on back to Frisco. An absorbing book, with respect for its ""incorrigible"" subjects and several bitter reflections about super-maximum security.