Triumph Without Victory : DEWEY DEFEATS TRUMAN By Thomas Mallon; Pantheon: 368 pp., $24

On the school picnic, one imagines, Thomas Mallon’s sandwiches would be cucumber and sardine instead of peanut butter and jelly. On the museum trip, he would be found in the basement examining the air-duct moldings. On the treasure hunt, he would come back, not with the Walt Disney video hidden by the teachers, but with somebody’s lost and badly missed pocket diary.

Mallon did, in fact, produce a splendidly antic book some years ago about diaries and how and why people keep them, as well as another about plagiarists and several novels. Although these last are not major works, each has some major minor memorable moments. If he were a wind-up toy, he would run in an engaging curve backward.

His “Dewey Defeats Truman” is a subjunctive novel, subjunctive denoting a contrary-to-fact condition. This is not remarkable in itself: A number of fictions have been written on such premises as, for example, Great Britain defeated and occupied by Germany in the Second World War.

What gives “Dewey” its genially antic twist is that it is conceived in the future subjunctive. It depicts a small-town world adjusting itself for an event it was certain would come to pass. In this case it is Owosso, Mich., living for months in anticipation of the certain victory of its native son, Thomas Dewey, in the 1948 presidential election.

It was not just Dewey’s hometown that was sure of the victory but most of the rest of the country as well. Dewey himself campaigned with the portly dignity of an incumbent, while Truman screeched and kicked like an outsider. This probably contributed to the upset, particularly since, when draped over the short, mustached, button-eyed Republican (“moist, canine eyes,” Mallon writes), portly dignity sagged like an out-sized suit.

The Chicago Tribune’s premature post-election headline, “Dewey Defeats Truman,” gives Mallon his title. What he is after, though, is not Owosso’s morning after, which takes up an offhand few pages at the end. The key to his amiable story is not shock, even among Owosso’s staunchest Republicans (some of whom loyally grew Dewey mustaches), but the sensation of awaking confusedly from an agreeable hallucination.

“Dewey Defeats Truman,” in fact, is about history taking a short break to dream itself differently. It is the alternate reality before reality sets in. Living out their assorted affairs and preoccupations, the characters have less than fictional weight. Regarded as fiction, in fact, Mallon’s book is rather thin and more than a little arranged.

His personages think of themselves as real, of course. We, knowing what lies ahead on the second Wednesday of that November, take them as figures more akin to those in a musical comedy than a novel; a musical less sunny than “Oklahoma” and not as shadowed as “Carousel.”

The triangle that jangles throughout Owosso’s wrong-way victory processional consists of Anne Macmurray and her rival suitors, Peter Cox and Jack Riley. Anne is a sprightly young woman who works in the local bookstore. She came to live in Owosso because she thinks it must be more “real” than Chicago or New York and thus ideal material for the great American novel she writes at night, a sentence or two at a time.

Peter, bumptious, rich and a junior at the local law firm, came to Owosso because it has a state Senate seat open. He has secured the Republican nomination and is campaigning dutifully for Dewey, enthusiastically for himself and, with growing passion, for Anne.

Jack, far too neatly his counterpart, unless you hold onto the musical comedy notion, is a union organizer and Democratic campaign worker. He is handsome, good in bed, idealistic and personally modest--and for most of the book Anne favors him while trying to suppress her yen for Peter. He, the apparent conservative, is the wild tiger, it turns out; Jack, the radical by Owosso standards, is a domestic puss.

The rivalrous romance moves along agreeably but somewhat dutifully; it doesn’t seem to be what Mallon is most interested in. As the preelection months wheel around like a revolving stage, the portrait of the town unscrolls, peaceable, provincial but forbearing. Like other “town” stories--Thornton Wilder’s Grovers Corners, Llareggub in Dylan Thomas’s “Under Milk Wood”--”Dewey” advances the stories of four or five characters more or less simultaneously.

There is the comic scheme to set up a Dewey memorial promenade along the town’s river, featuring such things as the chair used by the candidate when he was at law school and a papier-mache model of Dewey, as a New York prosecutor, leading a Mafia chieftain off to jail. There is the fierce opposition voiced by Col. Sinclair, an old widower who spends the day reading the classics and making his meals off the two roasted chickens he buys each week from a neighbor.

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Sinclair, a curmudgeon of taste and integrity, defends the river against the shoddy plans of the Chamber of Commerce. He has a second reason, spelled out in one of several stagy subplots. Another subplot, touching peripherally on Sinclair’s secret, concerns the passionate attachment of the teenage daughter of one of the town’s leading citizens to the moody, troubled Tim Herrick. Their story, closer to melodrama than to drama, ends reasonably happily after a series of incidents that include a disappearance and the stealing of a small plane.

In contrast, there is a lovely, complex portrait of Tim’s mother, Jane, who obsessively mourns her oldest son, killed in a brutal incident toward the end of the Second World War: the massacre by the Germans of 85 American prisoners during the Battle of the Bulge.

Glimpsed at first as a brooding eccentric, Jane is revealed gradually as the book’s most winning character. She has made herself a military expert, tracking virtually the minute-by-minute history of her dead son’s unit. Mourning is an activity of initiative and imagination; it is a celebration of memory and a subversion of the optimistic blandness of mid-century Owosso and America.

A prime bland example is the local paper. In its obituaries people do not die--they are “taken by death.” It made one feel, Mallon writes, that “all the dead in Oak Hill Cemetery were victims of a technical knockout, defeated perhaps, but crossing the bar like good sports.” Jane refuses to subscribe because she can’t stand the thump when the delivery boy throws it against her door “like a German grenade in the Ardennes.” Besides, “she had been troubled by the sense that whatever copy Billy threw was the wrong one.”

That is a haunting line; it is what Mallon does best. He is not a master of story or of the vectors of human movements and encounters. He writes the movements to notice the odd way a shoulder is held or an arm is swung, delineators of the quiet individual counter-eddies in the larger currents of history. Currents that, in the case of Owosso, are flowing blithely uphill.