US President George Bush has pledged to put an end to the FBI lapses that led to information on the US public being obtained unlawfully.
The FBI forced the release of information illegally or improperly
An internal report by the justice department on Friday said the FBI used the Patriot Act to force the release of information illegally or improperly.
It said most of the errors were through poor record-keeping or agent mistakes rather than criminal misconduct.
Democrats in Congress have vowed to investigate the report's findings.
"We'll address the problems in the report as quickly as possible," Mr Bush said at a news conference in Uruguay, where he is as part of a Latin American tour.
Rise in requests
The 126-page report by inspector general Glenn Fine said in some cases agents had failed to get the proper authorisation to obtain personal data.
In others, they sought the data in non-emergency situations.
The Patriot Act allows for the use of national security letters, or administrative subpoenas, in cases relating to spying or terrorism.
Under such a subpoena, personal records of clients and customers must be handed over to the FBI from such sources as banks, telephone firms and internet service providers.
The report said national security letter requests had risen from 39,000 in 2003 to about 56,000 in 2004 before falling back to about 47,000 in 2005.
In a review of field office files, the report found that 22% of the cases it investigated contained one or more possible unreported or unidentified violations.