WASHINGTON — Although the government’s warrantless surveillance program is associated with the National Security Agency, the Federal Bureau of Investigation has gradually become a significant player in administering it, a newly declassified report shows.

In 2008, according to the report, the F.B.I. assumed the power to review email accounts the N.S.A. wanted to collect through the “Prism” system, which collects emails of foreigners from providers like Yahoo and Google. The bureau’s top lawyer, Valerie E. Caproni, who is now a Federal District Court judge, developed procedures to make sure no such accounts belonged to Americans.

Then, in October 2009, the F.B.I. started retaining copies of unprocessed communications gathered without a warrant to analyze for its own purposes. And in April 2012, the bureau began nominating new email accounts and phone numbers belonging to foreigners for collection, including through the N.S.A.’s “upstream” system, which collects communications transiting network switches.

That information is in a 231-page study by the Justice Department’s inspector general about the F.B.I.’s activities under the FISA Amendments Act of 2008, which authorized the surveillance program. The report was entirely classified when completed in September 2012. But the government has now made a semi-redacted version of the report public in response to a Freedom of Information Act lawsuit filed by The New York Times.