AMERICAN PASTORAL By Philip Roth Houghton Mifflin. 423 pp. $26 WHAT BETTER place to contemplate the mysteries of identity than a 45th high school reunion? That's where Nathan Zuckerman, humbled by impotence and incontinence after prostate cancer surgery, finds himself at the beginning of Philip Roth's 22nd book, American Pastoral. This is a more subdued Zuckerman than in previous novels, shadowed and tugged at by death, as was the hero of Sabbath's Theater (1995) and the narrator Roth in Patrimony, his 1992 memoir of his father's final illness. Yet most of Zuckerman's old energy remains. Milling among his former classmates, Weequahic High School's class of 1950, he sets about assessing time's mutilation of the teenagers he once knew, observing erstwhile jitterbuggers now shuffling with canes, and a chubby-cheeked girl he groped on hayrides whose face is now "deeply scored as if with an engraving stylus." It's here that Zuckerman runs into a boyhood pal, Jerry, a guy who once tried to impress a girl by making her a coat out of hundreds of hamster skins. Shocked by the news that Jerry's brother has just died, Zuckerman retreats into his imagination. Quoting an old Johnny Mercer song ("Dream when the day is thru"), he dreams "a realistic chronicle" about Jerry's brother, the former Newark, N.J., sports hero Seymour Levov -- nicknamed the Swede because of his Nordic good looks -- and Zuckerman disappears to let the Swede's story take over. Before he goes, though, Zuckerman takes pains to describe just what the Swede, "the household Apollo of the Weequahic Jews," had once meant to him. He barely knew him, but to Zuckerman he was the enviable recipient of all the promises that postwar America made to the Jews of Newark. The Swede's father got rich manufacturing ladies' gloves; after a legendary high school sports career and a stint in the Marines, the Swede took over the business and made it even more profitable. He married his Irish college sweetheart, a former Miss New Jersey, moved to an old stone manor in the western Jersey suburbs, had a daughter named Merry whom he adored. The world, for the triumphantly assimilated Swede Levov, was his raw bar. Or was it? "You get them wrong," Zuckerman says about "this terribly significant business of other people"; "you get them wrong before you meet them, while you're anticipating meeting them; you get them wrong while you're with them; and then you go home to tell somebody else about the meeting and you get them all wrong again." It turns out that the Swede, this complacent golden boy "in love with his own good luck," is in fact a broken man, broken by the adolescent transformation, during the 1960s, of his beloved little daughter Merry into a fat, vengeful Fury who stuttered obscenities at her parents for being troglodytic capitalists, raged endlessly against the Vietnam war -- and finally bombed the local post office, killing a doctor who was there to mail his household bills. Merry goes on to live as a fugitive and a Jain, crazily committing herself to a life of squalor in the junky ruins of a Newark left smoldering and hopeless after its decimating riots, squatting in a hovel not far from the Swede's glovemaking factory. Her actions have sent her mother to a psychiatric hospital and her father to an even deeper, untreatable despair; she's transported him "out of the longed-for American pastoral and into everything that is its antithesis and its enemy, into the fury, the violence, and the desperation of the counterpastoral -- into the indigenous American berserk." USING this dialectic between the pastoral and counterpastoral American dream and American tragedy, Roth takes the story of the cheerfully hardworking, reasonable Swede and his frenzied Dionysian daughter into a broader social context, using his characters to represent three generations of American history which, with his Miltonian section headings, he calls the "Paradise Remembered" of the postwar period, "The Fall" of the ravaging 1960s, and the "Paradise Lost" of that decade's painful aftermath. The novel has the spaciousness and weight of an epic, a staggeringly successful one that manages to incorporate the day-to-day activities of glovemaking factories, the Miss America pageant, the raising of beef cattle and the radical revolutionary mind. But Roth's greater triumph here, in what is possibly the finest work of his career, is the thoroughness and intensity with which he plumbs the souls of his characters. One senses he's not so much writing about them as feeling them, probing every inch of their pain. And yet despite the compassion in his characterizations -- even the despicable Merry is a lost, pitiful child -- Roth's theme about the fundamental mysteriousness of people is achingly clear. "This was his daughter, and she was unknowable," thinks the Swede wonderingly. "This murderer is mine." "The fact remains that getting people right is not what living is all about anyway," Zuckerman muses. "It's getting them wrong that is living . . . That's how we know we're alive: we're wrong." It's breathtaking to witness an author at the height of his very considerable powers writing, as Roth does here, with so much humility and generosity and sorrow. Donna Rifkind writes frequently about contemporary fiction. CAPTION: Philip Roth