The Lunatic in Our Asylum : J. EDGAR HOOVER: The Man and the Secrets, <i> By Curt Gentry (W. W. Norton: $29.95; 760 pp.)</i>

In “J. Edgar Hoover: The Man and the Secrets” we get chilling proof that, given enough power, a single bureaucrat can poison an entire government.

Let me assure you that Curt Gentry is no Kitty Kelley. His goal, which he achieves, is not to sift through a life hunting only for what titillates, but to write a rounded biography, cradle to grave. It just so happens that Hoover’s cradle and grave were in Washington, D.C. He was a home-town boy, and there wasn’t much to say about him before he went to the Justice Department--unless you want to talk about his success as a high school cadet captain, or his speed as a delivery boy, or the boil that disfigured his nose--and there wasn’t anything to say about his life after he left the Justice Department, because he died there. The FBI was his life. What he did there, Gentry writes, was done partly as a super patriot, but also simply in defense of his hometown, to protect it from the evil world outside as he envisioned it.

If his actions were often warped, perhaps it was because, as Gentry tells us, “Except for the reports of his agents, he knew little of the rest of the world, or his own country for that matter, but he knew Washington as perhaps only a civil servants born of a long line of civil servants can . . . .” He knew almost instinctively that presidents come and go, that only the bureaucracy itself is enduring, and that it is the true foundation of the government.

He was to use “this knowledge with a brilliant skifllfullness to both establish and maintain his Byzantine power structure against all enemies for nearly five decades.” Awesomely researched and elegantly written, Gentry’s book is an absolutely fascinating study of the man who ran the Federal Bureau of Investigation for half a century. Lyndon Johnson once called Hoover “the greatest living American.” Dead (since 1972), he is memorialized in the costliest building in Washington. These are odd tributes for a public official who was, as Gentry so colorfully shows, an unbridled liar, a thief (he looted several FBI funds), a tax cheat, and a nonpareil hypocrite: While constantly prattling against pornography, Hoover enjoyed watching porn movies in his “blue room” theater, and among his prized possessions were miniature portraits of Eleanor Roosevelt, which, when turned upside down, resembled female genitalia.

But Hoover had a much more dangerous flaw, which many inside and outside the FBI noticed: He was, in a way, mentally deranged. One attorney general (the AG was, officially though not in fact, Hoover’s boss) thought he was just plain nuts. The Kennedys often spoke of Hoover’s “cartoonlike lunacy.”

They were not referring merely to his idiosyncracies--his compulsive hand-washing, his becoming unhinged at the sight of an unswatted fly, his insistence that agents not step on his shadow, his fanatical anti-fat crusade (one agent, writes Gentry, “was given a letter of commendation for single-handedly breaking up a Soviet spy ring, then fired because of his weight”).

They meant the kind of intense battiness, and threat, that Gentry best captures in this quote from an old FBI agent to a rookie, back in 1958: “You must understand that you’re working for a crazy maniac and that our duty . . . is to find out what he wants and to create the world that he believes in .”

Hoover and his minions created a world where people like Albert Einstein and justice Felix Frankfurter were judged to be dangerous radicals, where blind-deaf-mute Helen Keller was a security risk, where those cheerleaders of capitalism Dean Acheson and John J. McCloy were marked as members of “an enormous Soviet espionage ring,” where no one had a right to privacy (Hoover spied on his supporters as ruthlessly as he did his enemies), where blackmail and slander (especially if it had a sexual twist) were the nation’s first line of defense, and where the Red Menace--meaning not only “alien filth” but anybody on the left--was so overwhelming that the war against it called for the suspension of the U.S. Constitution.

Among the many clues to Hoover’s mental instability was his almost endless hate list. Blacks and Jews were at the top, but the British, French, Dutch and Australians were on it, too. He just didn’t like foreigners, and so far as is known, Hoover’s only trips outside the United States were two brief visits to a Juarez whorehouse (not for the purpose you might suppose). He hated Ivy Leaguers. A notorious “mother’s boy” (he lived with his until he was 43, when she died), he hated homosexuals, which may be because he was widely rumored to be homosexual himself, his constant companion being fellow bachelor and FBI associate, Clyde “Junior” Tolson.

Of the countless individuals Hoover hated, none made him froth so much as the often-bugged Martin Luther King, Jr. (whom Hoover described as “a tom cat with obsessive degenerate sexual urges”), Mrs. Roosevelt (whom he accused of having affairs with lesbians and with numerous male lovers, including at least one black), Robert Kennedy, and the godfather of the CIA, William J. “Wild Bill” Donovan.

Gentry documents how, at several crucial points in the nation’s life, Hoover’s hates cost us dearly:

* Because it came from British spies, Hoover withheld from President Roosevelt information that could have alerted him to Japan’s plans for attacking Pearl Harbor.

* The traumatic post-war witch-hunting era “was, from start to finish, the creation of one man”: Hoover. The infamous House Un-American Activities Committee and Senator Joe McCarthy received from the FBI all the raw data, scurrilous tips, and malleable witnesses needed to get headlines and create hysteria. The reverse side of Hoover’s help was that he did not leak to the press what he had heard about McCarthy’s weakness for bellboys and prepubescent girls.

* Hoover had known the Mafia was talking about killing the Kennedys, and Dallas FBI agents knew, as one of them admitted, that Lee Harvey Oswald “was capable of assassinating the President”--but they didn’t warn the Secret Service.

* Hoover, who had a “growing obsession with destroying” Martin Luther King, ordered his agents to stop warning King of assassination plots. When King was shot, agents in the Atlanta office, which had the primary responsibility for watching the civil rights leader, began shouting: “They got Zorro! They finally got the SOB!”

Hoover never associated with anyone socially unless he had something on them; some of his closest chums had links to organized crime, which may be why for most of his career he refused to let the FBI disturb the Mafia.

Instead, the FBI’s thousands of illegal wire-taps, bugs, mail-openings and burglaries were used to extort loyalty from, or ruin, politicians and other entertainers. No wonder Sam Rayburn called him “the worst curse that has come to government.”

The most shameful revelation of Gentry’s grisly autopsy is how gutless our politicians were. Congress, whose members Hoover routinely blackmailed, never once made an effort to curb him. As for the eight presidents Hoover served under, some wanted to fire him but dared not because, as Richard Nixon shouted into the White House tapes: “He’s got files on everybody, God damn it!”

Generally, the press was a stooge. Most journalists, seduced by leaks and planted stories, were content to glorify the FBI and smear its enemies. For a long time, Gentry writes, Hoover “could, and did, dictate what appeared in almost every newspaper in the United States.” The rare reporters (such as Jack Nelson of the Los Angeles Times) who uncovered FBI corruption, were vilified by Hoover as drunk skunks and vulture vomit.

Gentry tells us that of the eight young men who carried Hoover’s 1,000-pound casket into the capitol rotunda, two suffered hernias. It was symbolic of what the weight of this bad cop had done to the nation’s conscience.