By David Corn

St. Martin's. 370 pp. $25.95

This pot-au-feu of a thriller is brimming with gusto in spite of its familiar ingredients: Watergate, Chappaquiddick, the Kennedy assassinations, CIA scandals, congressional corruption and White House aide angst. Every old carrot and potato has been warmed over. Yet when you finish it, the palate wants more. How can this be?

Maybe it tastes so good because it's deepened with subtle tangs of Dante, the Apostle John, Robert Penn Warren and some heartbreaker '60s ballads. Or because, for all its derivative Washington insidering, there is no reference, not one, to the Monica Lewinsky mess. On the contrary, it's almost chaste enough--excepting frequent use of the F-word--to appease Lewinsky's namesake, the 4th-century St. Monica, pious mother of Augustine and patroness of matrimonial virtue.

The players are Washington characters and thus ought to be predictable. They suggest President Clinton, House Majority Whip Tom DeLay, Christian rightist Pat Robertson, House GOP Conference Committee Chairman J.C. Watts, soothsayer Dick Morris, CIA and FBI bosses, and many, many others. Yes, the usual suspects. But journalist David Corn gives them unexpected roles. At the same time, his wit and pace blow the town onto its ear.

Here's how it works. An assassin using the pass of a reporter he has killed attends a news conference and blasts the brains out of President Bob Hanover with a high-tech pistol. Then the wacko killer bites a poison ampule and dies without revealing his name. On his body he has recently carved the word "Happy" 17 times.

The ascending vice president, a revolting schemer, and the Washington establishment, particularly the FBI, would like for the blue-ribbon investigating commission to find only a lone killer. But enter Nick Addis, Hanover's most honorable, most guild-ridden aide, and not a particularly brave one, who is not buying the Oswald/Sirhan scenario. The ensuing plot, in both senses, is as fresh, shocking and bloody as guillotining.

Addis suspects that federal intelligence and law-enforcement agencies have ties to the assassin. His rapidly formed posse is made up of a beautiful, somewhat too-brilliant-to-be-believed CIA analyst, the disgraced head of the White House Secret Service detail, and a squirrelly ghetto Crew That Can't Shoot Straight. Their pursuit takes them into CIA headquarters, a macho gay club patronized by cowboy-dressed Marines, Blair House, the filthy lair of a one-eyed, car-bombing rummy and the room of a college student working as a look-and-talk-but-no-touch call girl.

Each time they begin to link the assassin to the FBI and CIA--and perhaps even the new president--their pigeon gets murdered. At last, by looking into a Whitewater-like case in Louisiana, Addis finds all the ingenious answers.

Among the techniques that enhance "Deep Background" are Corn's allusions to other books that cleverly lead us to reflect on his own. A quote from Robert Penn Warren, for instance, makes us think of "All the King's Men" and its real subject, Huey Long, the Louisiana populist demagogue who was also assassinated. It's a natural from there to muse on Long's younger, semi-loyal friend, so much like Addis, and then on into other parallels. There are other nice touches, such as the author's method for describing his hero. Every novelist faces the same problem. Do you have him look in a mirror? Have someone say, "Your gray eyes," etc.? Or just write lamely, "Joe Smith was slim, bronzed . . ."? Corn has us see Addis on the cover of a women's magazine, with a headline: "Tall, Skinny, Pale, Nerdy: A Sex Symbol for Now," with "a toothy, crooked smile . . ." Bingo. He's fixed in our minds.

The book is not perfect. Corn twice writes with seeming authority about ".9 mm" pistols. These would fire bullets tinier than a pinhead. He means "9 mm." And a successful con job to get a resident's key from an acting building manager is about as believable as spook Howard Hunt's red wig.

No matter. This first novel is as clean and steely as an icy Pinot Grigio. For example, when supporters of the new Christian right president hold up a banner saying simply "John 3:16," Corn does not explain. He challenges us to look up the citation and read it in the chillingly ironic context of the dozen or so good and evil people who perish murderously in this exceptional thriller.