WASHINGTON  Senior officials of the Federal Bureau of Investigation repeatedly approved the use of “blanket” records demands to justify the improper collection of thousands of phone records, according to officials briefed on the practice.

The bureau appears to have used the blanket records demands at least 11 times in 2006 alone as a quick way to clean up mistakes made over several years after the Sept. 11, 2001, attacks, according to a letter provided to Congress by a lawyer for an F.B.I. agent who witnessed the missteps.

The F.B.I. has come under fire for its use of so-called national security letters to inappropriately gather records on Americans in terrorism investigations, but details have not previously been disclosed about its use of “blanket” warrants, a one-step operation used to justify the collection of hundreds of phone and e-mail records at a time.

Under the USA Patriot Act, the F.B.I. received broadened authority to issue the national security letters on its own authority  without the approval of a judge  to gather records like phone bills or e-mail transactions that might be considered relevant to a particular terrorism investigation. The Justice Department inspector general found in March 2007 that the F.B.I. had routinely violated the standards for using the letters and that officials often cited “exigent” or emergency situations that did not really exist in issuing them to phone providers and other private companies.