Franklin Delano Roosevelt loved Lucy Mercer, his wife's social secretary. Mercer was young, beautiful, flirtatious and completely smitten with then-assistant secretary of the Navy Roosevelt. From 1916 to 1919, their relationship grew, especially during the summers when Eleanor Roosevelt took the five children away from Washington to the family's Campobello retreat on the Maine coast.

It was not a clandestine tryst. Although FDR tried to provide suitable escorts for Mercer in public, he rarely fooled any of his friends, who teased him good-humoredly. It is their stories that form the basis for the allegations of an affair.

While the record is a clear one of affection, there is no proven record of adultery. Despite the best efforts of historians, biographers and family members to uncover the paper trail of a sexual relationship, none exists. Eleanor Roosevelt burned the young woman's letters to FDR when she discovered them in 1919 as she unpacked her pneumonia-stricken husband's luggage. FDR's letters to Mercer have never been found. All that remains are titillating stories, anecdotes and sly comments -- the most famous being Alice Roosevelt Longworth's acerbic remark, "Of course, he deserved a good time. He was married to Eleanor."

In 1919, Eleanor Roosevelt offered her husband a divorce. Louis Howe, FDR's closest political adviser, and Sara Delano Roosevelt, his mother, strongly opposed it. Mercer's reaction is unknown, and the records of it conflict. What we do know is that Mercer was a devout Catholic, who well knew the church's sanctions against marrying a divorced man with five children. FDR promised his wife that he would never see Mercer again. Less than a year later, Mercer married Winthrop Rutherfurd, a 56-year-old widower with five children of his own.

Despite his promises to his wife, FDR did not let his married friend disappear from his life. He sent her tickets to the 1933 inaugural, arranged for them to meet at financier Bernard Baruch's estate and, after her husband died and with his daughter Anna's support, invited her to the wartime White House, where she presided over small dinners when Eleanor was out of town. She was with him when he suffered a fatal cerebral hemorrhage in Warm Springs, Ga., on April 12, 1945.

Lucy Mercer Rutherfurd was one of many women in FDR's life. He enjoyed and trusted women. His mother gave him unimpeachable love and support. Throughout his presidency, he developed close relationships with his sixth cousin Margaret "Daisy" Suckley, Princess Martha of Norway, and secretaries Marguerite LeHand and Grace Tully, all of whom have been the subject of rumors romantically linking them with FDR. He had solid working relationships with Democratic Party leader Molly Dewson, Secretary of Labor Frances Perkins, freelance reporter Lorena Hickok and a number of other strong women. And he was particularly close to his daughter Anna.

It was Tully who first publicly mentioned Mercer's presence, albeit inadvertently, in her 1948 memoirs. People began asking questions, but no one addressed them directly until Jonathan Daniels, the son of Josephus Daniels under whom FDR served as assistant secretary of the Navy, published two tell-all accounts of Washington life in 1954 and 1968. Every FDR biographer since then has struggled to reconstruct the relationship, before relegating it to two or three pages in their tomes.

And when the relationship was made public, if anything it enhanced FDR's image. Under attack by conspiracy-minded conservatives who believed he had concealed his role in the bombing of Pearl Harbor and more rational critics who argued that he had been too infirm to negotiate effectively with Stalin at Yalta, FDR's image was newly invigorated by evoca tions of his clandestine romantic rendezvous. After all, FDR was dashing.

The historical irony here is stark. In the hands of biographers and scholars, the FDR-Mercer relationship is most often used to explain Eleanor's activism rather than FDR's character. Either he was driven to Mercer because his wife was so little fun, or Eleanor was driven to activism because she was "a woman of sorrow," heartbroken by her husband's devotion to another woman -- a woman she had brought into her home as an employee. Furthermore, when Eleanor's close relationship with Hickok was revealed, many assumed that the FDR-Mercer love affair was sexual while Eleanor's with Hickok was not. In both cases, letters were burned, the record obscured and stereotypes triumphed.

While other presidents before and after FDR have been weakened by charges ranging from sleeping with a slave, to bigamy, to fathering an illegitimate child, to adultery, to entertaining dangerously unbridled sexual appetites, FDR escapes widespread condemnation. Why should this be?

Perhaps it is because we learned about Mercer years after FDR's death when his legacy, thanks in no small part to his wife's post-White House career, was firmly established. Perhaps it is because our image of Roosevelt the man is so inextricably linked to our surviving the two greatest crises of the century -- the Great Depression and World War II. Perhaps it is because we viewed Eleanor as "His Missus" and saw their marriage as the greatest political partnership ever to occupy the White House. Perhaps it is because his detractors did not need personal issues to incite their wrath: They hated the New Deal, and FDR's attempts to limit capitalism's excesses; and they hated Eleanor. Perhaps it is because of the fidelity shown him as father of the modern Democratic Party. Perhaps it is because of the intense emotional bond Americans developed with him through fireside chats and other forms of his outreach.

Or perhaps it is as simple as the press's decision to leave the president's personal life alone and focus instead on the strengths and weaknesses of his policies -- a degree of protection not available to more recent leaders. Whatever the reason, the record is as clear as it can be: FDR loved Lucy Mercer Rutherfurd when he was still a young man, and he continued to value her company and cared for her in the final years of his life. The same can be said of his feelings for his wife. FDR discarded other people close to him, but he did not abandon the two women he loved the most. FDR's relationships in politics and in love were never simple. The FDR-Mercer relationship illustrates just how complex the man's character was -- and how determined he was to follow his own code. Allida Black is the Finley fellow in history at George Mason University and the author of "Casting Her Own Shadow: Eleanor Roosevelt and the Shaping of Post-War Liberalism" (Columbia). CAPTION: FDR's relationship with Lucy Mercer Rutherfurd lasted from World War I until the time of his death.