The FBI repeatedly failed to follow the strict guidelines of the Patriot Act when its agents took advantage of a new provision allowing the FBI to obtain phone and financial records without a court order, according to a report to be made public Friday by the Justice Department's Inspector General.

The report, in classified and unclassified versions, remains closely held, but Washington officials who have seen it tell ABC News it documents "numerous lapses" and describe it as "scathing" and "not a pretty picture for the FBI."

FBI Director Robert Mueller is scheduled to brief Congress on the report at noon.

The officials say the inspector general found the FBI underreported by at least 20 percent the use of the controversial provision, known as National Security Letters, NSLs, in required disclosures to Congress.

The Patriot Act gave FBI agents the ability to demand telephone, bank, credit card and library records by issuing an administrative letter, bypassing the need to seek a warrant from a federal judge.

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Civil liberties groups have long opposed the provision, saying the lack of oversight could lead to the kinds of problems apparently uncovered by the inspector general. 

In a report last year, the Justice Department said there were 9,254 NSL requests on 3,501 persons in the calendar year 2005.

Some officials say the actual number is substantially higher.

The inspector general's report reportedly found "systemic" failures in the issuance, tracking and accountability of the controversial NSLs, although a Justice Department official said there was no finding of "willful or criminal misconduct."

FBI officials said they could not comment until the report was made public but said the FBI welcomed the findings because several of the reported problems were unknown to senior management.

"Expect a weekend firestorm," said one Justice Department official.