Welcome to Sleaze 101 : When James Ellroy starts explaining the Kennedy assassination, watch out : AMERICAN TABLOID, <i> By James Ellroy (Alfred A. Knopf: $25; 582 pp.)</i>

We’re smack in the middle of the Kennedy compound at Hyannis Port. Nov. 8, 1960. Election night.

“CBS called Illinois tight. NBC said ‘Cliffhanger!’ ABC said Jack would win, with 51% of the vote. . . . White phone 2 rang. It was Bobby with complaints. A journalist pole-vaulted into the compound. A hot rod sporting Nixon banners plowed the main house lawn. . . . The red phone rang. It was Santos Junior, with mob scuttlebutt. He said, Illinois looks dicey. He said, Sam G. threw some weight to help Jack. Lenny Sands was out stuffing ballot boxes. He had a hundred alderman helping him. . . . The red phone rang again. It was Pete, with more secondhand gossip. He said Mr. Hoover called Mr. Hughes. Mr. Hughes told him that Marilyn Monroe was quite naughty. The Feds had her hot-wired. During the past two weeks she banged disc jockey Allan Freed, Billy Eckstine, Freddy Otash, Rin Tin Tin’s trainer. . . .”

If anyone could beat “Hard Copy” and “A Current Affair” at their own game it would be James Ellroy, America’s incomparable B-movie novelist. His sprawling new book, “American Tabloid,” is U.S. political history as Sleaze Lit 101. It offers a lurid, “Twilight-Zone” vision of 1960s idealism, with enough government corruption and conspiracies to make Johnnie Cochran’s head spin. All the fallen idols of ‘60s pop culture are here, their hands in someone else’s pocket--Howard Hughes and J. Edgar Hoover, Jimmy Hoffa and Joe Kennedy, Santos Trafficante and Fidel Castro, J.F.K. and a naughty girl in every port.

Naughty by nature, that’s James Ellroy. Here’s his dossier: When he was 10, his mother, Geneva, was found in the bushes at Arroyo High School in El Monte, strangled to death. She’d last been seen boozing with a blond woman and a stranger the police called “The Swarthy Man.” After his father’s death a few years later, Ellroy spent a decade as a beatnik bum, drinking short-dog bottles of Thunderbird, smoking dope, reading crime paperbacks and sleeping in flophouses. In 1979, after he sobered up, he wrote his first crime novel, “Brown’s Requiem,” about a cop-turned-private eye enmeshed in a deadly extortion scheme. He sold the book--for $3,500--by sending an unsolicited manuscript to an agent listed in Writer’s Market.

Ten books later, Ellroy has emerged as a celebrated chronicler of low-life Los Angeles, his pulp-fiction sagas of 1940s and ‘50s-era LAPD and underworld depravity having grown grander and more graphic with each volume. His canvas is densely colored with complicated plot twists that send his fictional vice-squad cops into battle with true-life goons such as Mickey Cohen and Johnny Stompanato.

On the crime beat, no one can match Ellroy’s pungent, hepcat lingo. Hoods are “rackets overlords,” Miami Beach is “one big shiny bleach job.” He writes like Charlie Parker on the bandstand--his prose peppery and unpredictable, racing the edgy rhythm of a be-bop groove. When Jimmy Hoffa gets mad, he “pops double goosebumps and goes voodoo-eyed stuporous.” Everyone has a police-blotter nickname. In “American Tabloid,” Fidel Castro is the Beard, Robert Kennedy is Little Brother, J.F.K. is Jack the K, Bad Back Jack or Jack the Haircut.

But Ellroy is more than a literary jitterbugger. Underneath his tough-guy armor, he’s a writer with a strong confessional streak, a sucker for a compromised hero. Most of his brutish cops and thugs are riddled with pain and regret, carrying around the memory of a dead sibling, a father who went broke, parents who killed themselves. Perhaps Ellroy’s best-known book, “The Black Dahlia,” takes its inspiration from one of L.A.’s cult-classic unsolved murders, where the nude, mutilated body of a young woman is found in the weeds at 39th and Norton. As if there were any doubt about the kinship between this case and the author’s own childhood trauma, Ellroy opens the book with the dedication: “Mother: Twenty-nine years later, this valediction in blood.”

As his books became more violent, Ellroy’s style became more fragmented: 1992’s “White Jazz,” the last of a four-novel L.A. crime quartet, was a novel pumped out of a machine gun. Speedball prose: all staccato re-bop rat-a-tat-tat. Many critics found it unreadable, stymied by its dense telegraphic style and unrelenting savagery. It was Ellroy chomping at the bit to free himself from the straitjacket respectability of a detective fiction that had lost its razor’s edge. Today’s detective novel is as cozy and formulaic as Dorothy Sayers’ genteel mysteries were when Dashiell Hammett (to quote Raymond Chandler’s memorable phrase) “took murder out of the Venetian vase and dropped it into the alley.”

“American Tabloid” is Ellroy’s way of busting loose and leaving crime fiction--and Los Angeles--behind altogether. It aims high, interweaving a barbed-wire tangle of CIA assassination plots, Mob dope deals, scandal magazine rumormongering, FBI eavesdropping and Teamster pension fund corruption. Even the most dimwitted flatfoot could figure out the payoff. With Hoffa and the Mob seething over Bobby Kennedy’s Justice Department probes, with the CIA incensed over the Bay of Pigs fiasco, with J. Edgar Hoover desperate to protect his job--it’s only a matter of time before the dark forces converge on Dallas and stage a Hit Day for Jack the Haircut.

Ellroy makes the whole nasty business--the crime of the century, the assassination that spawned 30 years of increasingly fanciful conspiracy theories--feel as if it could’ve gone down as easy as sipping whiskey. “It can be made to happen,” says one plotter. “And it can be made to look like we weren’t involved.” Ellroy’s politicians and mobsters observe the same laws of the jungle. He subscribes to Malcolm X’s theory: The J.F.K. assassination is simply a matter of the chickens coming home to roost. But before he gets there, he gives you quite a ride.

As in earlier Ellroy books, the action revolves around a trio of lost souls: Pete Bondurant, a hulking ex-L.A. County deputy sheriff-turned-Howard Hughes bagman and free-lance shakedown artist; Kemper Boyd, an FBI undercover operative posing as a J.F.K. acolyte and CIA agent provocateur; and Ward Littell, a disgraced FBI agent turned mob attorney and J. Edgar Hoover informer. Alliances shift, relationships go sour--everyone has divided loyalties.

Like Oliver Stone and innumerable revisionist Kennedy biographers before him, Ellroy is obsessed with America’s loss of innocence. He sees J.F.K.’s brief ascendancy as a defining moment when idealism was overwhelmed by cynical sleaze-mongering, when Pax Americana principles degenerated into Cold War skulduggery, where the fabled Kennedy family values were a crude cover for rampant skirt-chasing. Ellroy doesn’t buy the high-toned New Frontier PR hustle. He places J.F.K. in the Oval Office on inaugural night, getting a pick-me-up shot and issuing his first presidential decree: “Find me some girls for later tonight.”

Boyd, the sleek FBI scoundrel, is Ellroy’s version of a Camelot-era smoothie, a “Best and the Brightest” pragmatist gone sour. A cutthroat Cold Warrior, Boyd uses his Justice Department civil-rights credentials as a cover for peddling heroin to poor blacks to help finance the Bay of Pigs invasion. In a way he’s J.F.K.’s doppelganger --a handsome charmer with no moral compass, his corruption echoing J.F.K.’s own fall from historical grace.

At its best, “American Tabloid” reads like a great Rat Pack backstage memoir. Ellroy sets his political history where the real action is--with J.F.K. and a babe at Peter Lawford’s beach house, gossiping about L.B.J. and Charles de Gaulle, with J. Edgar Hoover listening in on a bug hidden in the babe’s brassiere.

Ellroy’s true inspiration--and yet his biggest misstep--is to give this political history a tabloid spin, sketching his characters with the breezy literary shorthand you’d expect from a breathless “Hard Copy” reporter. It’s vastly entertaining, as far as it goes. But at nearly 600 pages, “American Tabloid” overstays its welcome. Sleaze Lit, like Tabloid TV, works best in sound-bite-sized portions. By definition, the tabloid sensibility is one-dimensional: long on sex and stimuli, short on depth and perspective. For someone like Graham Greene or E.L. Doctorow or Ward Just, the botched Bay of Pigs invasion might present an enticing opportunity to explore the hidden contradictions of America’s Cold War containment policy--or stand as a precursor of even more disastrous decisions to come in the swampy jungles of Southeast Asia.

But Ellroy isn’t a novelist of ideas. To him, the Bay of Pigs invasion is just a convenient showpiece to bring together his nutty ensemble of CIA dope dealers, Mob hoods, kooky Cuban exiles and Teamster thugs--he even drags a bunch of cracker Klansmen into the act. It’s a harmonic convergence of sleaze, but Ellroy is so intoxicated by his characters’ corruption that he doesn’t really wrestle with the consequences of their out-sized ambitions.

Maybe it’s asking too much for a writer so stoked by raw passion to make room in his tabloid universe for moral eloquence as well. As it stands, “American Tabloid’s” punch comes from its nasty ring of truth. Who’s to say that Ellroy’s tabloid imagination is further off the historical mark than other conspiracy theories? By deliberately blurring the lines between fact and fiction, Ellroy gives us is a nocturnal vision of American politics, whether it’s J. Edgar Hoover quoting Al Capone or Jimmy Hoffa plotting mischief, his cheap white sweat socks showing under his trousers. It’s a world where good guys are bad guys, bad guys are worse and the most patriotic guy of all is the CIA Cuban-refugee spy who arrives with a boatload of cutthroats, passing out Havana cigars and insisting that his first American meal be a sandwich at Wolfie’s Delicatessen on Miami Beach. In Ellroyland, just because you’re a scumball doesn’t mean you have to die hungry.