RABBIT AT REST By John Updike Knopf. 512 pp. $21.95

FROM NOW ON it is going to be hard to read John Updike without seeing all his earlier work as a long rehearsal for the writing of this book. Rabbit at Rest is that good. So often in the past, Updike's instinctively theological view of the world, his fall-of-each-sparrow style, his acute and squeamish sensuality, have seemed disproportionate to the job in hand. His three most recent novels -- The Witches of Eastwick, Roger's Version and S. -- have shown him as a writer content to toy with his tremendous gifts and squander them lightly on bright (and sometimes daffy) ideas. Now, with Harry "Rabbit" Angstrom at death's door, he has hit on a subject and a dramatic situation that have made him write for dear life. Rabbit at Rest is one of the very few modern novels in English (Bellow's Herzog is another) that one can set beside the work of Dickens, Thackeray, George Eliot, Joyce and not feel the draft.

Rabbit has served Updike well in the past as the quintessential American homme moyen sensuel in Run, Redux and Rich. As his surname was intended to signal, his heart was always troubled; it is now fatally diseased. He is old -- real old, in the American way. At the age of 55 he has been rendered obsolescent by the crowding generations. His unseemly paunch zipped into his plaid golf slacks, Rabbit is a great, decaying tub of memories . . . of high times on the basketball court, high times in the car trade, high times in bed with his neighbors' wives. He is a snowbird, summering in Brewer, Pa., and retreating for the winters to a seniors' condo block on the Gulf coast of Florida called Valhalla Village.

The book is set in three states, whose sawn-off names, FL, PA and MI, form the titles of its three decks. The third, short for Myocardial Infarct, is the state of mind and being in which Rabbit finds himself to be an appalled and unwilling resident. This new member of the United States (a populous territory, owing its power to candy bars, hot dogs, liquid lunches, frozen couch-potato dinners, car rides everywhere and other consequences of postwar American prosperity) bestows one singular privilege on its citizens -- an intense and apprehensive zest for the life of which it will, so very shortly, deprive them.

So Rabbit, always a greedy man, has never been so avid for sensation as now; and Updike, always a sensational writer (in the philosophical sense, "regarding sensation as the sole source of knowledge"), has never treated the tactile, pungent surface of life with the controlled abandon that he displays here. Together, author and character move through the book in a state of rapt attention and rapt memoriousness, tasting and sniffing the lees of Rabbit's life as if every sentence was likely to be the novel's last.

Plenty happens in Rabbit at Rest. Updike keeps the wheels of the plot (a cruel and ingenious machine designed to strip Rabbit of his dignity and leave him sans Toyota dealership, sans wife, sans family, sans libido, sans everything) going at full throttle through the long nights and days of these final weeks. But the story is there to enable the novel to do more important work; to create an epic, loving inventory of America as Rabbit has known it.

Rabbit, deep in the warren of his own thoughts, is a close cousin of Molly Bloom; and Updike has developed a wonderfully cuniculate, burrowing prose style for him to live in. Sentences loop nimbly from present to past and back to present again. Events of major importance (Rabbit's thoughts on the Reagan adminstration or on son Nelson Angstrom's cocaine habit) are eclipsed by events of even more major importance (Rabbit's thoughts on corn chips):

"KEEP ON KRUNCHIN', the crinkly pumpkin-colored bag advises him. He loves the salty ghost of Indian corn and the way each thick flake, an inch or so square, solider than a potato chip and flatter than a Frito and less burny to the tongue than a triangular red-peppered Dorito sits edgy in his mouth and then shatters and dissolves between his teeth . . ."

The great driving tension of the book comes from the way it continuously zig-zags across the fine dividing line between disgust and delight. It deals, at embarrassingly close quarters, with everything in America that is conventionally unlovable -- a life of ugly architecture, fast food, glop on television, billboards, ill-considered sex, the gulag of American marriage and the American family, the mortification of old age in a society enslaved to an ideal of youthfulness. Rabbit's life has been an averagely awful one; a fulfilment of all the worst prognoses in Toqueville's Democracy in America. Yet Rabbit, biting on a corn chip or a bar of Planter's peanut brittle, is able to extract from it all the sensuous immediacy of Keats bursting Joy's grape against his palate fine. The worst that America -- and Rabbit -- can do (which is to say, most of the nastiest, least esthetic, things in the history of civilization) is redeemed by the quality of attention brought to it, in wonder and humility, by such an American as Rabbit. THE BOOK emerges as a sustained theological test of agape, with Updike going into far deeper and more dangerous water than he has ever risked before. Brewer, Pa., in 30 years of fictive life, has become easy to love; the town has taken on the old-world charm of a Hopper painting. Deleon, Fla. is a much tougher proposition. Its cinderblock towers and thin Bermuda grass belong to a prefabricated, exploitative, developers' Aemrica that would challenge God's own powers to love the world. Rabbit, in his last extremity, finds himself situated in a landscape with no palpable history, no engaging nooks and crannies, and makes himself at home there by conjuring poignant sensations from such unlikely materials as the fake grain of the fibergalss hull of a Sunfish.

Two thirds of the way through the book, back in Brewer, Rabbit is enlisted to dress up as Uncle Sam and march at the head of his granddaughter's July 4th parade. Dressed in baggy striped pants, with a goatee scotch-taped to his chin, popping Nitrostats as he goes, Rabbit reviews his home town, its swarm of half-familiar faces, and, to the accompaniment of Kate Smith singing "God Bless America" from beyond the grave, he comes to the considered conclusion that: " . . . all in all this is the happiest {expletive} country the world has ever seen." It is a judgment won against all odds. Updike has spared nothing, either to the reader or to Rabbit himself. We have been plunged up to our necks in the dreck of late 20th-century America; we have suffered most of the indignities that old age and disease can heap on us. Yet Rabbit's unlikely affirmation sticks. Rabbit at Rest, on one level the story of a senseless wasting of life (Rabbit's terminal dive is linked, a shade too insistently, to the crash of Pan Am 103 at Lockerbie), is a happy book; an exultant hymn to the inexhaustible vitality of America, even here, even now.

It is a book that works by a steady accumulation of a mass of brilliant details, of shades and nuances, of the byplay between one sentence and the next, and no short review can properly honor its intricacy and richness. It must be read. It is the best novel about America to come out of America for a very, very long time. Jonathan Raban's books include "Old Glory" and the novel "Foreign Land." "Hunting Mister Heartbreak" will be published early next year. EDITOR'S NOTE: John Updike's three previous novels about Rabbit Angstrom -- Rabbit, Run (1960), Rabbit Redux (1971) and Rabbit Is Rich (1981) -- recently have been reissued in paperback by Fawcett Crest.