WASHINGTON — In its final week, the Obama administration has overhauled and lifted a veil of secrecy from rules governing the C.I.A.’s power to gather and use information about Americans, including setting new limits on what it may do with large sets of digital files that might contain private information.

The last time the government issued a comprehensive set of such rules — known as the Attorney General Guidelines because the Justice Department must sign off on them — was during the Reagan administration. They were classified, although some portions of them became public, as did parts of supplemental procedures added by subsequent administrations.

The Obama administration, after spending the last several years consolidating and rewriting the rules, has issued a new, comprehensive set, and it is making all 41 pages of the rules public.

“We are updating for the 21st century a set of rules that were previously not significantly updated since 1982,” Caroline D. Krass, the general counsel of the C.I.A., said in a briefing for several reporters at the agency’s headquarters. She called the rules’ release “a very significant milestone for the agency.”

The C.I.A. director, John O. Brennan, signed the new rules on Jan. 10, and Attorney General Loretta E. Lynch signed them on Tuesday. They are set to take effect in mid-March, 60 days after Ms. Lynch signed them. Because they are internal executive branch rules, President-elect Donald J. Trump’s administration could revise them again if it chose.

The C.I.A. is required to focus on foreign intelligence and leave domestic operations to law enforcement agencies like the F.B.I., but occasionally it obtains information about Americans or performs limited work on domestic soil.

It is difficult to compare the new rules with what came before because only pieces of the previous version of the rules had been made public through the Freedom of…