Americans loved Lucy, but Uncle Sam never forgot that as a young woman she declared herself a communist. Comedian Lucille Ball was hauled before Congress at the height of Sen. Joseph McCarthy's communist witch hunt. During a 1953 investigation by the House Un-American Activities Committee, Ball admitted that she had registered to vote as a Communist in 1936. But she said she did it to appease her socialist grandfather and that she was never an active member of the party. The committee forgave her, but J. Edgar Hoover never forgot. The FBI director continued to collect evidence about Ball, even though the FBI claims that it never officially investigated her. Our associate Scott Sleek obtained the Federal Bureau of Investigation's secret file on Ball and her first husband, Desi Arnaz. The file contains memos stamped "confidential" and addressed to Hoover. Many of the memos begin with "pursuant to your request," indicating that Hoover cared enough to keep personal tabs on Ball. Large portions of the FBI memos are blacked out because the FBI still considers them not ready for prime time. Here are some of the tidbits that FBI agents passed on to Hoover:The Daily Worker, a communist newspaper, alleged in 1951 that Ball was among the stars who had once been vocal in their opposition to McCarthy but then later kept their mouths shut.In February 1946, Arnaz appeared in a show sponsored by the Hollywood Independent Citizens Committee of the Arts, Sciences and Professions, a group the FBI said was a communist front.A Hollywood writer said that in 1937 she attended a Communist Party membership meeting at Ball's house. The writer said Ball was not there but had approved of the meeting.Hoover kept a clipping of an Associated Press story about Arnaz's arrest in 1959 for public drunkeness. Why would the FBI director be interested in Arnaz's police record? Hoover was notorious for collecting ammunition against his enemies to use for future face-offs, and a face-off with Arnaz was a distinct possibility. Arnaz headed Desilu Productions, which produced the TV show "The Untouchables." We have already revealed that Hoover despised the series because it credited Treasury agent Eliot Ness for feats achieved by the FBI. Hoover had his G-men monitor the show for mistakes. Ironically, Hoover said in a 1956 interview that Lucy and Desi were among his favorite stars. One of Hoover's fans took offense, and that letter is in the FBI file on Ball. "I'm wondering if there is not a mistake or misquote of some kind since it lists Lucy and Desi among your favorite entertainers who you think set a good example for the youth of America," the letter said. By the time Ball died in July, the communist witch hunt was a mere footnote to the praise. But Washington never forgets. In 1971, at the request of the Nixon White House, the FBI did a "name check" on Ball and her second husband, Gary Morton. The file doesn't reveal why the request was made, but the government routinely runs a check on the names in its files when someone is named to a federal post or invited to the White House.