“The literature on the Roosevelt era is immense,” Jean Edward Smith notes in his preface to “FDR” (Random House, 636 pages, $35), “there is little that has not been said, somewhere, about the president.” So why another biography? Because “Roosevelt himself has become a mythic figure, looming indistinctly out of the mist of the past.”

Mr. Smith aims to write not only history but also Plutarchian biography:

The “children’s hour” every evening when the president mixed martinis for his guests, the poker games with cabinet cronies, the weekly sojourns on the presidential yacht Potomac, and his personal relations with family and friends warrant extended treatment. Roosevelt enjoyed life to the full, and his unquenchable optimism never faded.

The biographer builds such an intricate network of personal detail that toward the end of the war, when President Franklin Roosevelt asks Eleanor to mix the martinis, we know Roosevelt is about to die. Anecdotes in this biography unmask FDR the man, with his shrewd ability to size up subordinates.

When the preening Douglas MacArthur kept Roosevelt waiting during the President’s trip to Pearl Harbor, FDR mildly asked the senior military advisers, “Where’s Douglas?” MacArthur then arrived seated in a very long, open touring car with sirens screaming and a motorcycle phalanx. “Hello, Doug,” Roosevelt said. “What are you doing with that leather jacket on? It’s darn hot today.”

Every Roosevelt biographer has to come to terms with how FDR’s polio affected the man and his policies. As Mr. Smith notes, for the last 23 years of his life FDR could not stand unassisted, let alone walk even a brief distance without the aid of heavy leg braces. How is it that this “Hudson River aristocrat, a son of privilege who never depended on a paycheck, became the champion of the common man”? The conventional explanation, Mr. Smith notes, is that overcoming personal adversity gave Roosevelt “insight into the nature of suffering.” True enough, but that analysis hardly explains the specific nature of FDR’s politics. Mr. Smith contends that the decisive influence was FDR’s exposure to the “brutal reality of rural poverty” in Warm Springs, GA., an experience that prompted him to help that third of the nation that was “ill-housed, ill-clad, ill-nourished,” to quote one of his most famous speeches.

It seems to me after reading Mr. Smith’s deeply moving biography that there is yet another reason for FDR’s empathy for the less fortunate: Here was a man with a powerful physique (massive shoulders, arms, and chest) who could not propel himself upward or forward, and who risked falling as he stood to greet world figures such as Stalin and Churchill. He expended more energy getting up than most people did in an entire day. He had the money to disguise his disability, to create the illusion that he could walk. But what of most other people who did not have his resources? That was the question that dominated Roosevelt’s politics and the reason he believed government had a role in providing equal opportunity for all.

Mr. Smith ranks Roosevelt with Presidents Washington and Lincoln as among this country’s greatest leaders. FDR’s creation of programs such as social security and the G.I. Bill have ensured his high position among presidents. But Roosevelt was also a great wartime leader. Mr. Smith credits FDR’s eight years as second-in-command in the Navy Department during the Wilson administration for FDR’s understanding of military organization, allowing him to make key decisions quickly and effectively. Better yet, he had taken the measure of figures such as George Marshall, Dwight Eisenhower, and Douglas MacArthur. By the time of the Pearl Harbor attack, FDR knew that these three men were indispensable, even though many other commanders outranked Marshall and Eisenhower.

Although FDR’s greatness is an indisputable theme in Mr. Smith’s book, this is no hagiography. If FDR did not invite the attack on Pearl Harbor, he certainly neglected the Pacific theater and pursued policies that, in retrospect, made the Japanese attack all too feasible, Mr. Smith argues. And about FDR’s court packing scheme — his attempt to add members to a recalcitrant Supreme Court that declared many New Deal measures unconstitutional — Mr. Smith is scathing. The issue was not a reactionary court, not a group of nine old men not up to the job, but a power-grab by a president who had overreached himself. Similarly, Mr. Smith is in no mood to exonerate FDR from the deplorable decision to intern Japanese residents during wartime.

FDR’s flaws notwithstanding, the epigraph to Mr. Smith’s biography, taken from Governor Cuomo’s keynote address to the 1984 Democratic National Convention, beautifully captures the greatness of the man and the leader: “He lifted himself from his wheelchair to lift this nation from its knees.”

crollyson@nysun.com