The book's back cover even carried (admittedly suspect) blurbs, like: " 'The author and his writings have been known to me for years' -- A penologist." For almost as long as there have been prisons, prisoners have turned author for diversion, creative expression, solace, penance, vindication, vengeance and release (physically and metaphysically). But their works have rarely been examined as a genre, and for what they reveal about the literary impulse behind bars.

Now, with more Americans than ever in prison, an exhibition at the John Jay College of Criminal Justice of the City University of New York is doing just that in a survey of American convicts' writings titled "Inside Editions: A Literature of Punishment." Some of the work, like Malcolm Braly's 1967 book, "On the Yard," is uncommonly good. Indeed, the American Center of PEN, the writers group, is in the 28th year of a program that sends authors into prisons to lecture and arranges publication of the best of the 1,500 prison manuscripts submitted each year.

Chester Himes, the author of "Cotton Comes to Harlem," wrote his first short stories while serving time for armed robbery in the 1920's and 30's. Edward Bunker, who at 17 had been the youngest inmate ever in San Quentin, emerged to write a string of gritty, well-received novels of prison life, including "No Beast So Fierce," which was made into the 1978 movie "Straight Time" with Dustin Hoffman, and "Animal Factory," just made into a television movie starring Willem Dafoe. Mr. Bunker was also a co-writer of the 1985 Oscar-nominated movie "Runaway Train," starring Jon Voight.

One of the best, and most famous, prison writers was Eldridge Cleaver. In a 1963 essay for a prison newsletter, he explained to his fellow inmates at San Quentin how important reading had become for him. "A library is the center of the world," he wrote, "a point transcending time in which the past, present and future converge in a flash of light." The prisoner may have painted himself into a corner, or society may have painted him in, but through reading, Cleaver said, "we will cease to sell and allow ourselves to be sold short, having grown so large that a painted corner, a prison cell, can't contain us." Five years later he published his scathing confessional, "Soul on Ice."

But generally, when you talk of American prison writing, you are not in the league of great literature, certainly of nothing like the writings of Boethius, John Bunyan, Dietrich Bonhoeffer, Aleksandr I. Solzhenitsyn or other prisoners of conscience whose words have illumined their unjust cells and all mankind. (One exception is Henry David Thoreau.) Prison writers, by and large, are felons, convicted killers, robbers and con artists linked by an urge to memorialize a wayward life, a survival strategy or a religious conversion, and in the process, to entertain.

The works in the John Jay exhibition were collected by the college's chief librarian, Larry E. Sullivan, a professor of criminal justice in the City University's Graduate School and a former librarian at the Maryland State Penitentiary in Baltimore. They range from earnest tracts to lurid sexploitation paperbacks portraying lascivious-looking women ("Reform School Girl!," "Passion Behind Bars"). Or, for the gay market, there are hunky male prisoners in skivvies ("Caves of Iron").

"I bought them for the covers," confessed Mr. Sullivan, who holds a doctorate in medieval studies from Johns Hopkins and claims he has the largest private collection of American convict literature, some 350 first editions. "I also collect depressing prints of the Depression," said Mr. Sullivan, himself the author of a book not written in prison: "The Prison Reform Movement: Forlorn Hope."

A sampling of the convict writings suggests that it doesn't take long for a new inmate to become a penologist. In 1798, Stephen Burroughs, a thievish New England schoolmaster with a nasty weakness for seducing his young charges, found himself in prison in Worcester, Mass. He didn't care for it much, Burroughs wrote in his "Memoirs," the young republic's first known work of prison literature. In fact, he found prison downright counterproductive, "the most perfect school of vice that I ever saw.

" Prison proved a strong reality check, too, for Nathaniel Hawthorne's son, Julian. In 1893 he had ghosted a prisoner's story that included a cover drawing of a man behind bars and the legend "By This Method the Law Protects Society." But 21 years later, when the younger Hawthorne was himself in the Atlanta federal penitentiary for mail fraud, he wrote "The Subterranean Brotherhood," in which he called for an end to penal servitude. Many if not most prison memoirs qualify as confessionals, extended mea culpas, often with strong religious overtones and purplish prose.

In "Shadows of the Gallows," Patrick C. Murphy does not stint in airing his shame and dread. He began, "You shall hang by the neck until you are dead, dead, dead are the dying echoes that hover around me as I stand in the shadow of that grim instrument of death."

Contrition (along with some gloating) also went into the prison memoir of Emmett Vestal, alias "Texas Slim." Vestal was twice condemned to death yet lived to recount his misdeeds with the Tom Slaughter Gang and its fearsome boss ("even his name spelled death"). His 1934 memoir, "Ten Years in Hell," exemplifies what Mr. Sullivan called "the 'Bible against machine gun and the Bible always wins' genre."

Some works boil down to, "I'm here because of my social class," a category tellingly defined by Donald's Lowrie's 1912 classic, "My Life in Prison," which presaged some of the writings of the black radicals of the 1960's and 70's. And many prison memoirs serve as survival strategies, with the authors frequently citing Friedrich Nietzsche's famous aphorism "That which doesn't kill me makes me stronger." Mr. Sullivan said that the subtext often is, "I'm getting stronger, and I'll get you when I get out."

In any case, prison writing is flourishing these days. In his latest book, "Education of a Felon," an autobiography just published by St. Martin's, Mr. Bunker described a scene of frantic literary activity behind bars: "The loudest sound is of scattered typewriters, each with a different speed and rhythm, from stilted uncertainty to an unbroken pulse, from petitions for writs of habeas corpus to the Great American Novel, for I am not the only Folsom convict who dreams of redemption via the literary life, of making a lotus grow from the mud."