WASHINGTON — FBI Director Robert Mueller struggled yesterday to convince skeptical senators that — despite recent abuses — the FBI should retain Patriot Act authority to gather telephone, email, and financial records without a judge’s approval.

“The statute did not cause the errors. The FBI’s implementation did,” the FBI chief told the Senate Judiciary Committee.

But the committee chairman, Senator Leahy, a Democrat of Vermont, served notice: “We’re going to be re-examining the broad authorities we granted the FBI in the Patriot Act.” House Judiciary committee members delivered a similar message last week.

The panel’s ranking Republican, Senator Specter of Pennsylvania, went further: “The question arises as to whether any director can handle this job and whether the bureau itself can handle the job.”

Grim-faced and sometimes even looking pained, Mr. Mueller testified at the panel’s second hearing into a Justice Department inspector general’s report this month that detailed abuses in the FBI’s use of documents called national security letters to gather data.

Reviewing headquarters files and four of 56 FBI field offices, Inspector General Glenn Fine found 48 violations of law or presidential directives during 2003–2005. He estimates there may be up to 3,000 unidentified or unreported violations throughout the FBI.

Mr. Mueller said he had instituted procedures for issuing these letters. “What I did not do and should have done is put in a compliance program to be sure those procedures were followed,” he added.

He is now devising a compliance program and has ordered an audit to determine the extent of the problem and to see if any agents should be disciplined.

“We are committed to demonstrating to the committee, the Congress, and the American people that we will correct the deficiencies,” Mr. Mueller said.

“I still have very serious qualms,” Mr. Leahy replied.

Mr. Mueller called the letters “an indispensable tool for our conduct of terrorism investigations” and began listing cases in which the letters were useful, including a plot against the Brooklyn Bridge.

Interrupting, Mr. Leahy said the panel could discuss individual plots later, including “how serious a plot it was to take down the Brooklyn Bridge.” Government court documents acknowledged that defendant Iyman Faris, now serving 20 years in the case, advised Al Qaeda the plot would be futile.

Citing the national security letters and recent inspector general criticism of FBI reporting of terrorist cases and of weapons and laptops lost, Mr. Specter said, “Every time we turn around there is another enormous failure by the bureau.”

Mr. Specter said the committee should seriously consider establishing a separate domestic intelligence agency like Britain’s MI-5.

“There’s another headline virtually on a daily basis,” Mr. Specter said, citing a Washington Post report yesterday that agents submitted inaccurate data to a court that issues warrants for foreign intelligence surveillance.

Mr. Mueller said he had reduced such inaccuracies since learning of the problem in 2005 but noted that warrant applications are long and contain thousands of facts.

“I’m not impressed with your assertion that there are thousands of facts,” Mr. Specter said. “That’s your job. You asked for these powers; we gave you them. If these applications are wrong, you’re subjecting people to an invasion of privacy that ought not to be issued.”

The committee plans to hear April 17 from Attorney General Alberto Gonzales, now struggling to keep his job amid criticism of the FBI abuses and the firing of eight U.S. attorneys.

National security letters, first authorized in 1986, can be used to acquire e-mail, telephone, and travel records and financial information, like credit and bank transactions.

In 2001, the Patriot Act eliminated any requirement that the records belong to someone under suspicion. Now, an innocent person’s records can be obtained if FBI field agents consider them relevant to an ongoing terrorism or spying investigation.