The new novel is Don DeLillo's wake for the cold war. According to its argument, the discontinuity in American cultural life had a primary cause: nuclear weapons. The hiatus was inaugurated on the day that Truman loosed the force from which the sun draws its powers against those who brought war to the Far East, and was institutionalized four years later when the Soviet Union started to attain rough parity. Cosmic might was now being wielded by mortal hands, and by the State, which made the appropriate adjustments. The State was your enemy's enemy; but nuclear logic decreed that the State was no longer your friend. In one of the novel's childhood scenes, the schoolteacher (a nun) issues her class dog tags:

''The tags were designed to help rescue workers identify children who were lost, missing, injured, maimed, mutilated, unconscious or dead in the hours following the onset of atomic war. . . . Now that they had the tags, their names inscribed on wispy tin, the drill was not a remote exercise but was all about them, and so was atomic war.''

Nuclear war never happened, but this was the nuclear experience, unknowable to anyone born too soon or too late. In order to know what it was, you have to have been a schoolchild, crouched under your desk, hoping it would protect you from the end of the world. How people rearranged their lives around this moral void, with its exorbitant terror and absurdity, is DeLillo's subject. Perhaps it always has been. The new novel, at any rate, is an 827-page damage-check.

''Underworld'' surges with magisterial confidence through time (the last half century) and through space (Harlem, Phoenix, Vietnam, Kazakstan, Texas, the Bronx), mingling fictional characters with various heroes of cultural history (Sinatra, Hoover, Lenny Bruce). But its true loci are ''the white spaces on the map,'' the test sites, and its main actors are psychological ''downwinders,'' victims of the fallout from all the blasts -- blasts actual and imagined. DeLillo, the poet of paranoia and the ''world hum,'' pursues his theme unstridently; he is tenacious without being tendentious. Yet even his portraits of bland, hopeful, pre-postmodern American life -- his Americana -- glow with the sick light of betrayal, of innocence traduced or abused. The ''great thrown shadow'' has now receded and terror has returned to the merely local. MAD (Mutual Assured Destruction) was exploded; and the bombs did not detonate. Still, the press-ganged children who wore the dog tags must live with a discontinuity in their minds and hearts. DeLillo's prologue is called ''The Triumph of Death,'' after the Breughel painting. In the end, death didn't triumph. It just ruled, for 50 years. I take DeLillo to be saying that all our better feelings took a beating during those decades. An ambient mortal fear constrained us. Love, even parental love, got harder to do.

The protagonist, Nick Shay, works for a company called Waste Containment. And ''Underworld'' is among other things a witty and dramatic meditation on excreta, voidance, leavings, garbage, junk, slag, dreck. A drunken spectator at the 1951 Dodgers-Giants playoff leans forward and disgorges a length of ''flannel matter. He seems to be vomiting someone's taupe pajamas.'' A newlywed on his honeymoon finds that ''his BMs'' (daily ''hygiene'' is another euphemism) ''are turning against him'': ''that night Marvin had to make an emergency visit to the hotel toilet, where he unleashed a fire wall of chemical waste.'' This is human waste, forgivable waste. But then there is nuclear waste: the stuff that never goes away and makes heaven stop its nose. In the exceptionally inspired epilogue, entitled ''Das Kapital,'' Shay visits the Museum of Misshapens in Semipalatinsk and confronts fetuses preserved in Heinz pickle jars. Then he visits the radiation clinic and sees, among others, a ''woman with features intact but only half a face somehow, everything fitted into a tilted arc that floats above her shoulders like the crescent moon.''

In ''White Noise'' the famous ''airborne toxic event'' was the result of a military-industrial accident. But it was also DeLillo's metaphor for television -- for the virulent ubiquity of the media spore. Explaining a recent inanity of his daughter, Shay's co-worker ''made a TV screen with his hands, thumbs horizontal, index fingers upright, and he looked out at me from inside the frame, eyes crossed, tongue lolling in his head.'' DeLillo's way with dialogue is not only inimitably comic; it also mounts an attack on the distortions, the jumbled sound bites, of our square-eyed age. ''I'll quote you that you said that.'' ''She's got a great body for how many kids?'' ''They put son of a bitches like you behind bars is where you belong.'' ''I'm a person if you ask me questions. You want to know who I am? I'm a person if you're too inquisitive I tune you out completely.'' ''Which is the whole juxt of my argument.''