PIECES OF TIME: The Life of Jimmy Stewart.<i> By Gary Fishgall</i> .<i> Scribner: 416 pp., $27.50</i>

In the spring of 1941, with 28 movies to his credit and an Oscar for “The Philadelphia Story,” a 6-foot, 3-inch but underweight James Stewart coaxed his draft board to accept him. He would be in the military, ready to do his bit. The Oscar could sit on a shelf at his dad’s hardware store in Indiana, Pa. Stewart was 33, as deft at comedy as at romance and a balance of Ivy League manners (he had been to Princeton) and country innocence. America was learning to see him as a fresh version of Gary Cooper, a poet of hesitant speech and bashful sincerity, the sort of Mr. Smith whom Washington needed. So this star folded up his career and drew the line on a series of romances that had included Ginger Rogers, Norma Shearer, Olivia de Havilland, Eleanor Powell and even Marlene Dietrich. He did the right thing.

Suppose that man had died on any of the 20 bombing missions he flew (and often led) over Germany. Losing that kind of lieutenant colonel, with a Distinguished Flying Cross as well as an Oscar, would have been more drastic a loss than even Glenn Miller. We might look at his movies then--at “The Philadelphia Story,” “It’s a Wonderful World” (a neglected comedy), “Destry Rides Again,” “Mr. Smith Goes to Washington” or “The Shop Around the Corner” (with Margaret Sullavan, perhaps the woman he loved best back then, but she was always married to someone else)--and marvel that this muddled country of ours, so obsessed with and dishonest about image, could achieve so unsullied an icon. Stewart had an unforced purity in his frank, amused eyes and his tender, drawling voice.

Of course, he came back from the war. He was not too well at first: His nerves were shot; he lived on a diet of sweet, pulpy foods; and he had to move in for a while with his old buddy Henry Fonda. Like many survivors, he was altered and scarred. Then he lived another 50 years, with all the chances they offered to mar his spotless reputation. Stewart died just a few months ago, leaving us to congratulate ourselves for having at least one American we could love without reservation. He was a decent, honorable guy, so subtle and humane an actor that his nobility never announced itself or seemed to beg. We could gauge Stewart’s character from the way he listened, responded, talked and even watched, as in “Rear Window.” Never part of the Method, Stewart still gave every sign of being locked in thought and self-examination. His voice became the sport of mimics and comedians, but it was the imprint of his wondering eyes that we remembered. His charm as a talker (on women and men) should not be underestimated: During the war, Stewart often led the briefings on big raids, and a young soldier, Walter Matthau, liked to sit in just to enjoy the ease and fun of his talk.

Nevertheless, war did change Stewart, and it is a failing in Gary Fishgall’s decent, methodical and very fond book that this shift is inadequately described. In the decade and a half that followed the war, Stewart delivered a series of ambiguous, flawed heroes who are hardly matched in American film and stand as question marks after the ineffably likable guys he created in the 1930s: George Bailey in “It’s a Wonderful Life,” the small-town model who, at the thought of failure, tries to kill himself; the bleak loners he played in the Anthony Mann westerns, from “Winchester ‘73” to “The Man From Laramie”; the two portraits of inquiry on the edge of obsession done for Hitchcock in “Rear Window” and “Vertigo”; and even the politico who faces his own fraud in John Ford’s uneven “The Man Who Shot Liberty Valance” (a role for which he was plainly too old).

It’s not that the actor slipped from Dr. Jekyll to Mr. Hyde. His darker characters are older brothers to the sweet guys who preceded them. They have the same respect for hope and an unwavering, gentle alertness to others, but doubts have seeped in, along with gray in the hair. The cheerfulness is more wistful; the attentiveness is not as open or trusting. There are signs of blame, vengeance and selfishness; he is lonelier in ways nothing can mend. This is the kind of development in an actor’s career (and face) that we no longer see or journey with. But it makes Stewart all the more compelling that the imperiled (and self-pitying) idealism in “Mr. Smith Goes to Washington” could lead to the emotional tyrant in “Vertigo.” He was essential to some of the most problematic and momentous films ever made in America. Run “Mr. Smith” and “Vertigo” side by side, and you have not just a display of an actor’s growth or talent a demonstration of how the best movies once learned to see through their own concept of “the good guy.” To enjoy the movies made today, without shadow or shame, you must forget such experiments and the profound elusiveness in Stewart.

Stewart is not obvious material for a biography; he behaved too well. Writing about his virtues can turn into homilies about the sweet, professional, caring man he was, and Fishgall lays this mist on thick, unaware how swiftly it burns off. Yes, Stewart was courteous to others; he stayed true to his small-town ideology and revered his father. He married late, to Gloria McLean, but married well and was faithful, and together they raised their children to lead useful lives. He was conservative and Republican, and when one of his sons was killed in Vietnam, Stewart saw the tragedy in terms of “our boy and so many like him [being] sacrificed without having a unified country behind them.” His restraint speaks to a lack of melodrama not common in actors and not that helpful to a biographer.

In other words, there were movies in which Stewart’s characters were more searching than he was in life. There’s no reason to be surprised by that. It is part of our weird adoration of actors that we endow them with more wisdom than they have. The Stewart who emerges in this thorough, if uncritical, book is a straightforward man, one who confessed he wasn’t smart enough to direct or produce movies and who had little of interest to say about his complex roles.

Fishgall’s method rather abets this reticence. For instance, when he writes about “The Man From Laramie,” it is not enough to say: “Particularly memorable were a couple of brutal sequences, one in which Stewart is roped and dragged through a campfire and the other in which he is shot in the hand at close range.” That scene in Mann’s western is really one extended sequence, and it has a power not evoked by this account: Stewart’s nice guy could suggest outrage, damage and cruelty enough to justify retribution. The sequence cries out for fuller exploration just because it reveals a capacity for pain and passion that Stewart was too polite or too well-raised to talk about.

Fishgall does admit that Stewart had one limitation. “He was a good boy. But, perhaps in being so obedient, he became more submissive in adulthood than was advantageous. He was a hard worker, but affability, raw talent and a pleasing appearance--plus a fair amount of very good luck--took him further in the theater and later in films than ambition ever did.”

Even the loftiest stars were the pawns of a studio power that controlled their destiny (Stewart rarely challenged the MGM system that made him, even though his agent Lew Wasserman later made pioneering profit-sharing deals for him). Stewart generally did as he was told. He came along at the prime moment for his folksy nobility to be put to tougher tests; that’s why “It’s a Wonderful Life” was a gift of casting and timing. It was a return to the dream for Stewart, who after five years away had seen things in life that hardly fit the dream. It was a movie in which two men, Stewart and director Frank Capra, allowed the thought that movies had not been asking the right questions about life and society.

There’s some sadness in this book as the rather passive “natural” actor lets his career go flat in the early 1960s and struggles to stay active before succumbing to deafness, melancholy and the emptiness that followed the death of his wife in 1994. He wrote rather dire verse that became a best-selling book because of the huge public affection for him. He didn’t really do a worthwhile picture in his last 35 years. That hardly matters. Yet it is telling: We cannot conceive the same abdication of energy or risk in, say, Burt Lancaster, Laurence Olivier or Jack Nicholson. But Stewart waited to be asked, and it is likely that he did “Vertigo,” “Rear Window,” “The Naked Spur,” “The Far Country,” “The Man From Laramie,” “It’s a Wonderful Life” and “Anatomy of a Murder” with the same mix of diligence and feeling of luck that resulted in more ordinary films like “The Glenn Miller Story,” “The Greatest Show on Earth” (he played a clown, in makeup, throughout the picture), “The Stratton Story” (as a baseball pitcher who loses a leg), “Harvey” (that sentimental favorite in which he chatted to a large, unseen rabbit) and even “The Spirit of St. Louis,” a really awful movie (his second favorite, after “Wonderful Life”) in which he played Charles Lindbergh--talking to a fly in the cockpit.

Our fondness mixed all those movies together, too, and we reveled in the delight at what a good actor could do in the 1940s and 1950s. But in that first list of movies above, I suggest, there are glimpses into the troubled soul that America and this book are still too young for. George Bailey’s nightmare haunts us all now, way beyond the wondrousness of life and the sturdiness of small savings and loans.