Under the Freedom of Information laws, New York Times correspondent Mitgang has, over the last few years, obtained government records (primarily FBI files) relating to some three-dozen writers and authors. Parts of these files have been held back (for ""security reasons""); others have been drastically censored. Only four files concern living writers. But what Mitgang has compiled here is enough to document what was suspected for decades: that J. Edgar Hoover's FBI, and other US agencies, monitored the writings, statements, and actions of prominent writers (""left-wingers"" especially), sometimes using surveillance, mail-checks, and other privacy-invasive tactics. The basic facts--already revealed in news stories and in anew Yorker excerpt--are disturbing. The details, and Mitgang's preachy commentary, are less riveting. Predictably, the files contain references to liberal views espoused, groups joined, meetings attended, foreigners met, petitions signed; Robert Lowell's file, like those of many others, records his anti-Vietnam War stands; personal problems, like John O'Hara's drinking, are sometimes mentioned; the sources range from newspaper clippings to unnamed informants and vague rumors. A few of the files offer up fascinating vignettes: an exchange of letters re FBI procedures between Hoover and Archibald MacLeish; the FBI's reactions to Rex Stout's devastating anti-FBI thriller, The Doorbell Rang. Overall, however, the brief dossier-summaries--including run-downs on Sinclair Lewis, Pearl Buck, Faulkner, Hemingway, Steinbeck, Elmer Rice, Maxwell Anderson, Edmund Wilson, Norman Mailer, and W.H. Auden--hold few surprises, and more chuckles than shockers. A chapter on artists features Alexander Calder, Ben Shahn, and Georgia O'Keeffe--who raised typically foolish suspicions by voting for Henry Wallace and entertaining Asians. And the FBI's inanity is most amply displayed in the section on publisher Alfred A. Knopf. Mitgang lays out the gathered material with little focus or shape. Worse yet, his excessively polemical approach tends to undermine the documentary evidence--which speaks very well for itself. Lamely sarcastic asides are relentlessly tossed in to highlight the file-writers' literary ignorance and the thinness of their accusations. In the heat of righteous indignation, some writers' political histories--Lillian Hellman's, for instance--are white-washed. And Mitgang's tirades against the Reagan-Meese administration and its predecessors occasionally slip over the edge from well-meaning to weak-minded--as when the sorry state of today's TV (commercialism, etc.) is blamed on 1950's blacklisting. An important story, then, but a dullish, uneven book.