<i> FDR: A Biography by Ted Morgan (Simon & Schuster: $22.95; 905 pp., illustrated)</i>

Franklin Delano Roosevelt had no schoolmate until he was 14 years old, for it was the custom among the wealthy families of Hyde Park to have their children properly tutored.

There were arithmetic tutors, language tutors, music tutors. When among Franklin’s peers one lad climbed a tree with swift skill, his chums surrounded the boy, asking: “Who is your tree-climbing tutor?”

Privilege, in F.D.R.’s world, was accompanied by the relentless scrutiny of his mother, Sara. Even when he became managing editor of the Harvard Crimson, Sara wrote letters urging him to spend time outdoors, for the air of the Crimson office was not fresh.

F.D.R. found ways to protect himself against his mother’s possessiveness, to dissemble and adapt without giving up his inner coherence. He knew how to flatter her need to be indispensable. He also knew how to hide his true feelings from her.

How he did it, and how he climbed one formidable barrier after another on his remarkable odyssey from a sheltered, privileged childhood to become a champion of populist causes and the only four-term President of the United States, is the subject of this carefully crafted biography by Ted Morgan.

A French-born, Pulitzer Prize-winning reporter who changed his name from Sanche de Gramont in 1977 when he became a U.S. citizen, Morgan has previously written perceptive biographies of Winston Churchill and Somerset Maugham.

Morgan demonstrates with clinical detail and colorful anecdotes that F.D.R. probably absorbed the political nuances of punishment and reward from his mother, for Sara was the boss of her own machine, dispensing patronage and cutting off the undeserving.

One time she promised a string of pearls as a birthday gift to a granddaughter, Betsy Cushing. But minutes later, when Betsy failed to be attentive, Sara said: “I’ve been thinking of what I could give you that would be more suitable and I know just the thing--paper napkins.”

F.D.R. learned well the lessons of patronage. When at 31, after serving briefly in the New York legislature, he was appointed assistant secretary of the Navy in the Wilson Administration, he made his office a clearinghouse for requests from New York contacts, and he operated as a broker for federal jobs out of the Navy department.

His political instincts were jarred occasionally by his wife’s candor. Once, early in World War I, under the headline “How to Save in Big Homes,” a New York Times story quoted Eleanor at length on a food-saving program for her family of 7 and her 10 servants. The Roosevelts made good use of leftovers, Eleanor said, adding: “Making the 10 servants help me do my saving has not only been possible but highly profitable.”

In a fury, F.D.R. wrote to Eleanor, who was vacationing at Campobello: “Your latest newspaper campaign is a corker and I am proud to be the husband of the Originator, Discoverer and Inventor of the New Household Economy for Millionaires! Please have a photo taken showing the family, the 10 cooperating servants, the scraps saved from the table and . . . I will have it published in the Sunday Times.”

For much of his life, however, F.D.R. proved skillful at courting the press. He did not always mean what he said: He was a man in search of a bandwagon, yet in public and private he tried to appear pursued instead of the pursuer. In 1920, shortly before he was nominated for the vice presidency, he wrote to his law partner: “I am not at all sure that I care for it.”

Again in 1928, on the eve of his nomination to be governor of New York, he wrote to his mother: “I have had a difficult time turning it down.” Soon after his arrival in Albany there was speculation that he would run next for the presidency, and he wrote of his dismay to an old friend: “I am really concerned by talk about 1932.” In 1940--before he won a landslide victory over Wendell L. Willkie--F.D.R. pretended to be cool about the notion of seeking a third term, and he even seemed to encourage others to run. As a result, so many Democratic hopefuls stepped forward that The New Yorker offered some deadpan advice to its readers: “Nominate your friend for President. It makes a charming and inexpensive Christmas gift.”

But there was, of course, much more to the man than demure denials. Endowed with style, wit and charm, impelled by accomplished role models (including his cousin Theodore), F.D.R. reached a turning point at age 39, in 1921, when he was stricken by polio.

The permanent paralysis of his legs marked the start of a maturing process on two levels: from a sense of privileged entitlement to a fervent belief in duty and public service, and from political dilettante to true professional.

His longtime aide Steve Early said later: “If it hadn’t been for his affliction, he never would have been President of the United States. In those earlier years, he was just a playboy. . . . He couldn’t be made to prepare his speeches in advance, preferring to play cards instead. During his long illness, he began to read deeply and study public questions.”

F.D.R. became an extraordinary student of history, and his eagerness to read, combined with his instincts for leadership and responsiveness, enhanced his talent for governing. “There were no isolated events for Roosevelt,” Morgan writes, in this engrossing and comprehensive portrait of the complex personality who led America through the Depression and World War II. “Everything that happened in the state and the nation, every crisis, every decision taken, was part of a larger context of America fulfilling its destiny, of an experiment in government still being worked out.”