Congress is moving to limit use of “national security letters,” an information gathering technique that has increased dramatically since passage of the USA Patriot Act after the terrorist attacks in 2001.

The letters require companies to provide private information about their customers and to keep the request secret. The FBI issues more than 30,000 such letters annually, compared with about 300 a year before the Sept. 11, 2001, attacks.

Legislation authorizing renewal of the Patriot Act have added a level of judicial review for such letters, which currently can be approved by any of about 60 senior FBI officials and which receive no routine scrutiny from the courts.

A key limitation included in a tentative deal worked out by House and Senate staff members would also require the FBI to destroy or return records obtained with secret intelligence warrants if the subjects turn out not to be connected to terrorism or some other crime.

Jeff Lungren, a spokesman for House Judiciary Committee Chairman F. James Sensenbrenner (R-Wis.), acknowledges staff members are negoating limits to the Patriot Act.

The American Civil Liberties Union, part of an unusual coalition of liberal, conservative and business groups opposed to some of the surveillance and search powers contained in the Patriot Act, praised the proposed Senate restrictions but said stronger limits are needed on the use of national security letters.