TOWARD THE END OF TIME.<i> By John Updike</i> .<i> Alfred A. Knopf: 342 pp., $25</i>

Now in his middle 60s, John Updike has always seemed to know a little more about the lives of his contemporaries than we did ourselves. He wrote of childhood’s fair and apprehensive mornings, of earthly appetites, metaphysical glimmerings, the cocksure boundlessness of young married life, the erosion of all these things and the autumnal color, fall and wind-drift of our certainties.

With wicked mastery of the moment and insufferable prescience, he laid out the course of time’s booby-traps. Sure enough, it was not long before his aging readers would stumble into them.

Now, God help us all--or all of us pensionables--he announces old age. Not the mythical old age of his first novel, “The Poorhouse Fair,” with its silvery, otherworldly procession of ancients. His latest book catches up with the procession, and it is us: raging, unquiet and disintegrating.

“Toward the End of Time” is a self-narrated year in the dwindling life of Ben Turnbull, a 66-year-old retired investment counselor with a home on 11 expensive acres north of Boston. Updike lives in the same posh neighborhood, and in this book he includes several other aspects of his own life as well. Clearly he had not exhausted his stock of rabbits with the celebrated tetralogy of that name. He has just pulled one more out of his headgear.

Through Turnbull, Updike discerns anger and fear as the main features of old age. They lodge in the sense that the world has changed, that it is no longer familiar or graspable, that it has been ruined and taken over by strange and hostile forces. And the author uses an ingenious device to suggest all this.

He sets Turnbull’s advancing senectitude not in the present but in the year 2020. China has attacked Japan with nuclear weapons, and the United States has destroyed China, while incurring severe but only partial damage itself. California is ruined and so is the Midwest. New York still functions, and New England has pretty much been spared.

Boston is shabby and decaying from a slowed-down economy, but the only hit it took was from pro-Chinese saboteurs who blew up City Hall and the Federal Building next to it. No great loss since Bostonians, as Updike knows, detest them both. New England is actually doing fairly well selling seafood and apples to the rest of the country. Lacking a national tax base, the federal government is all but inoperative, so a local currency has been issued. It is called the Welder, after Massachusetts’ recent governor and never-to-be ambassador to Mexico.

We begin to realize that Updike’s future comes with a considerable wink. His devastation is erratic, even frivolous. Turnbull’s wife runs a thriving gift shop; they drive good cars and employ a gardener. He still goes into Boston to churn a portfolio or two, drops in at the Ritz and plays country club golf. His grown children and stepchildren have decent careers and come home for Christmas and Thanksgiving.

Updike has only a playful interest in future-games. What he has done is devise a kind of objective correlative for the growing sense of helplessness, disconnection and indignity that can assail old age. Turnbull’s erratic world--comfortably normal at times and at times wrecked and unrecognizable--acts as a projection of the alternate failings and rallyings of mind and body as the human condition weakens into its end.

Turnbull’s ordeal is recorded in a journal beginning in November just as winter approaches, and ending a year later when winter suggests the death of something more than a cycle of months. His most conspicuous and touching struggle is with Gloria, his second wife, who has acquired more energy and command as the years pass and his own powers dwindle. An entrancing example of Updike’s affection for furious women, she appears more and more threatening to him. Even though she monitors his health, he feels she is ruthlessly adjusting to what he sourly calls her “emerging widowhood.”

She conducts open warfare against the deer that stray in and eat the plants, pelting them with golf balls and borrowing a shotgun which, she insists, Turnbull is to use against them. He begins to identify with the deer; they seem to represent the freedom and beauty that his aging has deprived him of.

As he weakens, with sporadic assertions of energy and will, his journal records a growing number of episodes that drift away from the tangible realities of his life with Gloria. They open into a cloudy conundrum. Turnbull, who has read with fervent unsteadiness in the popular versions of contemporary physics, conjures up such things as wormholes, time reversal and alternate realities.

With a conviction that dwindles along with his strength--at the end he is impotent and incontinent after a devastating prostate operation--he records a number of such alternate realities. He becomes a grave robber seeking gold in ancient Egyptian burial chambers. He is the apostle Mark, arguing religion with St. Paul. He is an Irish monk-scribe being massacred by Viking marauders.

Nearer home, he writes of shooting Gloria and taking as his mistress Deirdre, a former deer who has become a young prostitute and charges him so many Welders per discrete sexual favor. The protection racket thugs who extort a monthly fee for “guarding” his property--without federal subsidies the local police are useless--turn exorbitant until they are blown away by a band of teenage killers who take over. As part of the service, they grant Turnbull fondling privileges with one of their girl gang members.

Updike allows his protagonist some extensive theorizing about his alternate worlds. But, as with the oddly sporadic presentation of a post-nuclear future, we sense that the author is pointing elsewhere. Turnbull’s wormhole escapes, which flicker cloudily and slip back unstably--Gloria turns up with deer repellent after being “killed”--are indistinguishable from the fantasies of an aging mind.

This makes for some fairly dry work. The balance between giving life to a story and talking at it leans to the side of talk--particularly since it is hard to provide vital distinctness to alternate worlds when you suggest that they may be mental constructs. Some of them--the grave robbing, for example--are hardly more than whimsical.

Yet, seen not for themselves but as part of Turnbull’s aging struggle, the fantasy alternate worlds are truly affecting. Stripped of vitality and power, the failing protagonist makes a final grab for command by using the loopy metaphors of physics to declare reality for the cloudiness of his mind and desires. In his rage against the “dying of the light,” he elevates the imminent end of his particular time into the astrophysical hypothesis of the End of Time.

It is bombast, but Updike has the mercy to treat it as one more set of clouds, and he accords Turnbull a clearing chink of humility. His “alternate worlds” alternate with his occasional notes about the lovely mortality of this one: a patient record of the flowers and plants in his garden, a recollection of the feel of a grandson’s hair.