The timing was thus significant when, one night in 1946, F.B.I. agents dropped by his house overlooking Sunset Boulevard and told him that Communists were infiltrating a liberal group he was involved in. He soon had a new purpose; as he wrote, “I must confess they opened my eyes to a good many things.”

The newly released files flesh out what Reagan only hinted at. They show that he began to report secretly to the F.B.I. about people whom he suspected of Communist activity, some on the scantiest of evidence. And they reveal that during his tenure as president of the Screen Actors Guild in the ’40s and ’50s, F.B.I. agents had access to guild records on dozens of actors. As one F.B.I. official wrote in a memo, Reagan “in every instance has been cooperative.”

Reagan went on to make his fight against Communism in Hollywood a centerpiece of his talks as spokesman for General Electric in the 1950s. Those eventually became broader warnings about what he saw as creeping socialism. The founding fathers, he declared in his 1961 speech, believed “government should only do those things the people cannot do for themselves.”

But that guidance apparently didn’t apply to Reagan himself. According to F.B.I. records, in 1960 he turned to the federal government for help with the kind of problem families usually handle themselves. That March, his close friend George Murphy reached out to an F.B.I. contact, explaining that Reagan and Ms. Wyman, now divorced, were “much concerned” about their estranged daughter, Maureen, then 19. She had moved to Washington, and, her parents had heard, was living with an older, married policeman.

According to an F.B.I. memo: “Jane Wyman wishes to come to Washington to perhaps straighten out her daughter, get her back to Los Angeles, but before doing so desires to know the following: (1) Is [the man in question] employed as an officer of the Metropolitan Police Department?; (2) Is he married?; (3) Is his wife in an institution and what are the details?; and (4) Any other information which might be discreetly developed concerning the relationship.”