VIGNETTE. A June day in 1864, on the bloody battlefront in Virginia. Some 5,000 Union soldiers have just fallen in an assault at Cold Harbor. A visitor dines with General Grant and observes that his face "gives no expression of his feelings and no evidence of his intentions. He smokes constantly, and . . . has a habit of whit[t]ling with a small knife." William McFeely quotes this observation in one of the insightful asides that deepen and enliven this fine book. "Is this the definitive photograph of Grant?" he asks. "Does it fix him forever as calm and earnest, sensibly keeping his fingers busy as he concentrates . . . Or is it the picture of a profoundly vacant creature . . . unable to conceive of the terrible dimension of the martial enterprise in which he is engaged."

Just so. Grant is a historical riddle, and McFeely, who writes with a skill one welcomes but doesn't expect from a history professor, admits that his only reason for writing yet another Grant book was his urge to take a fresh crack at the problem; to "take him [Grant] seriously as a man."

The mystery is simple enough. How could someone be so good in war and so inept in peace? Grant was a rural Ohio youngster whose close-fisted tanner father got him into West Point hoping that the Army would furnish a livelihood for his boy, who had no business sense whatever. Grant was graduated in time to marry, serve competently in Mexico from 1846 to 1848, then start a family. But garrison life ruined him. His efforts to piece out skimpy pay with business sidelines were flops. Enforced separation from his beloved Julia and the children drove him into depression and drink. So he quit in 1854, came home, botched various ventures arranged for him by kinfolk, and in 1861 was working in a tannery owned by Papa in Galena, Illinois. He was a 39-year-old manchild on the edge of poverty, sensitive, reclusive, happier in the company of horses than of men. Assets: a loyal wife and a few good friends. Prospects: none.

Then the war and destiny arrived simultaneously. West Pointer Grant got a regiment to command, and raced up the ladder of success that had kept collapsing under him as a civilian. He managed almost everything correctly -- the battles, the political infighting, the morale needs of citizen soldiers, the special problems of terrain that might require daring maneuvers around Vicksburg one year, and costly slogging towards Richmond the next. He learned from his mistakes. Contrary to legend, he rarely drank. He knew what he was doing and why. Wartime photos show him leaning against a tree or sitting on a bench with a writing pad on one knee carelessly flung over the other. Reposed, unassuming, no strut about him, nor an ounce of self-doubt.

So he brought the republic the victory it wanted and needed, and in return it bestowed on him (as it likes to do on the right generals) the presidency that he wanted and needed, since, as McFeely opines, there was no way he could go back down to Galena and all that it meant.

What he did go back to was failure. His two-term administration had a few accomplishments, but against them had to be set the undoing of Reconstruction, a major split in the Republican Party, a depression, scandal after scandal involving his close friends and appointees in the War and Treasury departments, and suspect associations with sleazy promoters trying to engineer a corner on gold, a Caribbean landgrab. He left the office branded for historians as a catspaw to spoilsmen.

After which came more collapses and a final triumph. A bid for a third-term nomination in 1880 did not succeed. Then he lent his name to a shaky business venture which crumbled into bankruptcy and criminal prosecution for one of its partners. But in 1884 Grant was offered a good sum to do his memoirs, just as he learned that throat cancer was going to kill him in short order. His final year of life was a race against pain, feebleness and the calendar, but he finished his book and infused it with a tautness and clarity that made it a minor classic. Even in recollection, war sharpened his attention and skills.

What does this inconsistent pattern prove? Was Grant evidence of democracy's failure, as Henry Adams suggested in his snobbish comment that one could not simultaneously believe Grant and evolution? Or, on the contrary, did Grant confirm democracy's potential, by showing that an ordinary man, given a chance, could be extraordinary and match achievements with history's greatest and most titled captains? Earlier studies were divided between the Grant of the muckrakers, and the Grant of those who, Whitman-like, saw him and his war as proof of young America's marvelous vitality.

McFeely's reading of the record is different. He sees in Grant a man of his time, beset by the terrible fear of failure and hardship that swallowed so many around him, especially those who, like him, did not do well at the all-absorbing game of getting. For if the fluidity and opportunity of pre-1861 American life were marvellous, they showed a darker side as well. In a world without the automatic status of a feudal order, or the built-in securities provided by the modern welfare state and corporation, winning economically was, in fact, the only thing. Those men who did not succeed by the sole accepted yardstick -- the making of money -- were condemned to a life of boredom, possibly relieved by drunkeness or cruel amusements or religious zealotry, a slow stifling of love for a faded spouse and cheated children, a long endurance of the pity or scorn of successful neighbors. Grant, McFeely says, probably saw that kind of future before him in 1861, yet knew (or shared the national faith) that he was cut out for better things if he only got the right break. He got his break when the firing started. Thereafter he could not let success go. He sought a presidency for which he was unqualified because "he could not risk giving up an inch for fear that he might fall all the way back."

It is a provocative view, to some extent afloat on main currents in recent research into 19th-century family patterns, class structure and symbolic roles. If there is a problem, it is that McFeely must conjecture much, since first-hand testimony on the state of Grant's mind from Grant himself is rare. Much of his Grant may be in his imagination. But after all, it is works of the imagination that the Civil War has had its greatest impact on us as Edmund Wilson pointed out in Patriotic Gore. And what McFeely has produced in Grant: A Biography is, in fact, better than a biography. It is, in the true sense, a "life."