THIS PEN PORTRAIT and album of photographs of Franklin D. Roosevelt is one of the most delightful and thoughtful commemorations of the 100th anniversary of his birth. Joseph Alsop, drawing in part upon his memories both as a member of the extended family of Roosevelts and as a young newspaperman in New Deal Washington, deftly illuminates the public and personal sides of Roosevelt.

The portrait, for all the warts, is favorable; Alsop deems Roosevelt "one of the great Presidents in the classical mold," comparable to George Washington in that he was twice needed and twice responded. It was Roosevelt who led the nation first through the ordeal of the Great Depression, then through the dangers of World War II.

To his contemporaries, even those who knew him best, the president was hard to fathom. He was charming, full of enthusiasms, warm and generous toward others, apparently a thorough-going extrovert--yet a part of himself remained ever remote and private, even from those closest to him. Then there was the problem that at close hand Roosevelt seemed so often to be careless, superficial, and even misleading in conversation. Even his admirers endlessly cite Justice Holmes' alleged appraisal that his was a first-class temperament and a second-rate mind. His detractors are far more harsh.

Much of the condescension, Alsop notes at the outset, came from those close to him in the White House, who regarded him as an essential but frequently misguided force, "always in need of being guided and manipulated, of being aimed like a fire hose." One is reminded again of Washington, with his wholly different personality, whom Hamilton regarded as the essential aegis (protector and sponsor). Yet, Alsop gently suggests, quite the opposite seems to have taken place. Roosevelt used his advisers, and when they had served his purposes, would put them aside for others. They in all their talented, quarrelsome variety, were an aegis for him.

The goals toward which Roosevelt labored, first in peace and then in war, were noble ones. His achievement in foreign policy, when the forces typified by Hitler were unleashed, was to convince his fellow countrymen that the United States no longer enjoyed eternal security behind the barrier of two great oceans. The most singular achievement domestically, Alsop thinks, transcending even the inauguration of the welfare state, was his fight to attain full rights for all those previously excluded in an essentially WASP America. It was a singular undertaking for one who had been brought up so securely among the white, Protestant gentry.

For Roosevelt to transcend a background in which, as his wife Eleanor once noted, one was taught that "New York society was important," was in itself a remarkable feat. Alsop, himself of that same background, is particularly adept in portraying that world of Edith Wharton as he remembers it. Alsop's mother regarded Franklin as so unduly handsome that she sometimes referred to him as "the handkerchief box young man," and thought him not good enough for her first cousin Eleanor.

At least, this account makes clear, Roosevelt was singularly insensitive to his wife's feelings of inadequacy, and while they both shared noble aspirations he was far less intense, and more fun-loving in his social life. A rift was slowly developing during the years he was Assistant Secretary of the Navy in the Wilson administration, even before he became smitten with the lovely Lucy Mercer. Alsop reports some fresh family gossip concerning that notable romance, but adds little to the denouement. Roosevelt promised to stop seeing Lucy Mercer; Eleanor Roosevelt continued to be married to him, but suffered an abiding feeling of being betrayed.

Nonetheless, the Roosevelts supported and reinforced each other as he fought to come back from a crippling polio attack and she cast aside her shyness to undertake a public career. Through three terms in the White House, it was an unparalleled partnership in search of great ends. After his death she recalled Roosevelt's achievements with great admiration. She did not, as Alsop states, try to mislead this writer by showing him affectionate letters from her husband written in 1917 or 1918; any miscalculation was the biographer's own.

There is more than Eleanor's side to the story. Alsop has learned that during World War II when Roosevelt resumed his relationship with Lucy he shared all his diplomatic and military secrets with her. Hence, Alsop concludes, the love affair must have been profoundly important to him, that earlier Roosevelt would have abandoned family and career for Lucy if she, a devout Catholic, would have had him. Not all evidence points in this direction, but the experience had certainly been a searing one for young Franklin as well as for his wife. For whatever reasons he did not break off his marriage or his political career, and he kept to himself whatever pain he suffered.

Out of the crucible of the fight to recover from polio (coming after the failed romance), he proved himself resilient. Optimism about finding a way out, tough obstinacy in refusing to accept defeat together with "his magical sense of political timing, and his remarkable astuteness in avoiding showdowns until a showdown was likely to produce a satisfying result"--these were, Alsop suggests, "a recipe for as formidable a political leader as the United States has known in the 20th century."

There were shortcomings in Roosevelt's administration of both the New Deal and the American effort in World War II, and Alsop reports them, even as he does the achievements. The casting of accounts is impressive, but the book is even more memorable for its candor, delightful style, and fresh evidence. Roosevelt appears less as an enigma and more as a quite human person with his share of weaknesses, and far more than the ordinary strengths--boundless confidence, intelligence, and skill in perilous times.