The FBI has increasingly used administrative orders to obtain the personal records of U.S. citizens rather than foreigners implicated in terrorism or counterintelligence investigations, and at least once it relied on such orders to obtain records that a special intelligence-gathering court had deemed protected by the First Amendment, according to two government audits released yesterday.

Because U.S. citizens enjoy constitutional protections against unreasonable searches and seizures, judicial warrants are ordinarily required for government surveillance. But national security letters are approved only by FBI officials and are not subject to judicial approval; they routinely demand certain types of personal data, such as telephone, e-mail and financial records, while barring the recipient from disclosing that the information was requested or supplied. ....