Congressional Republicans and Democrats on Wednesday challenged Attorney General Eric Holder over the Justice Department's handling of the investigation of national security leaks and its failure to talk to The Associated Press before issuing subpoenas for the news service's telephone records.

In exchanges that often turned testy, Holder defended the inquiry while pointing out that he had removed himself from any decision on subpoenas. The attorney general explained that he had been interviewed about what he knew of national security developments that prompted the probe.

The investigation follows congressional demands into whether Obama administration officials leaked secret information to the media last year to enhance the president's national security credentials in an election year.

"It's an ongoing matter and an ongoing matter in which I know nothing," Holder told the House Judiciary Committee.

The Justice Department secretly obtained two months of telephone records of reporters and editors for the AP, seizing the records for more than 20 separate telephone lines assigned to the AP and its journalists in April and May 2012.

Holder defended the move to collect AP phone records in an effort to hunt down the sources of information for a May 7, 2012, AP story that disclosed details of a CIA operation in Yemen to stop an airliner bombing plot around the anniversary of the killing of terrorist leader Osama bin Laden.

The attorney general called the story the result of "a very serious leak, a very grave leak." Earlier this week in a statement, AP President and Chief Executive Officer Gary Pruitt called the gathering of phone records a "massive and unprecedented intrusion" into how news organizations gather the news.

Under questioning, Holder said he recused himself from the investigation though he couldn't provide the panel with the exact date nor did he do so formally in writing. He said he was unable to answer questions on the subpoenas and why the Justice Department failed to negotiate with the AP prior to the subpoenas, a standard practice.

"The telephone records would not disappear if the AP had been notified," said Rep. Zoe Lofgren, D-Calif. "How could it ever be the case?"

The frustration extended to Republicans and Democrats.

"There doesn't appear to be any acceptance of responsibility for things that have gone wrong," Rep. James Sensenbrenner, R-Wis., told Holder. He suggested that administration officials travel to the Harry S. Truman Presidential Library and take a photo of the famous sign, "The buck stops here."

It was the Justice Department's No. 2 official, Deputy Attorney General James Cole, who made the decision to seek news media phone records, Holder said.

Last year, Holder appointed two U.S. attorneys to lead a Justice inquiry into who leaked information about U.S. involvement in cyber-attacks on Iran and an al-Qaida plot to place an explosive device aboard a U.S.-bound flight. Holder had resisted calls for a special counsel, telling lawmakers that the two attorneys, Ron Machen and Rod Rosenstein, are experienced, independent and thorough.

Holder was grilled on several scandals rocking the administration, including the targeting of conservative groups by the Internal Revenue Service and any missteps in sharing intelligence information prior to the bombings in Boston.

Holder said the FBI's criminal investigation of the Internal Revenue Service could include potential civil rights violations, false statements and potential violations of the Hatch Act, which prohibits federal employees from engaging in some partisan political activities.

In one of the sharpest exchanges, Holder defended Thomas Perez's tenure as head of the Justice Department's Civil Rights Division and said he would make a great secretary of the Labor Department.

Rep. Darrell Issa, R-Calif., was critical of Perez and repeatedly pressed Holder, who at one point refused to stop talking and accused Issa of repeatedly mischaracterizing the work of the Justice Department.

"That is inappropriate and is too consistent with the way in which you conduct yourself as a member of Congress. It's unacceptable and it's shameful," Holder told Issa.

The congressman ignored the comments and continued to question Holder.

Toward the end of the hearing, in another fierce exchange with a Republican lawmaker, Holder said that despite any personal animosity toward him, the office of attorney general deserved some respect.

He bemoaned the "toxic partisan atmosphere" and said "a level of civility doesn't exist."

Responding to news of the gathering of AP records, Sen. Chuck Schumer, D-N.Y., said he was reviving a 2009 media shield bill that protects journalists and their employers from having to reveal information, including the identity of sources who had been promised confidentiality.

The bill does contain some exceptions in instances of national security.

"As we've seen with the recent subpoena of the AP records, there is a real need for some statutory guidelines about what kind of information the government can get from the media. Right now there is virtually no guideline, there's no supervision," Schumer told reporters. "Our bill is carefully crafted. I spent many, many months negotiating between the Newspaper Association of America and the White House and finally we came to an agreement."

Schumer said the bill provides an independent evaluation by a judge, but he conceded that he was unsure whether it would apply to the leak investigation and AP phone records.

"I don't know the facts of this specific case, but I do know this, that everyone would have felt a lot better had there been an independent arbiter as to whether any information should be required of the AP and how much, how broad the request should be," the senator said.

The White House threw its support behind the push Wednesday morning, with Ed Pagano, President Barack Obama's liaison to the Senate, placing a call to Schumer's office to ask him to revive the bill _ a step the senator had planned to take. White House spokesman Jay Carney said Obama "believes strongly we need to provide the protection to the media that this legislation would do."

Obama's support for the bill signaled an effort by the White House to show action in the face of heated criticism from lawmakers from both parties and news organizations about his commitment to protecting civil liberties and freedom of the press.

White House officials have said they are unable to comment publicly on the incident at the heart of the controversy because the Justice Department's leak probe essentially amounts to a criminal investigation of administration officials.

It's not clear whether such a law would have prevented the government from gathering the AP phone records as it would depend on the provisions in the bill and how they were written.

Sen. Dianne Feinstein, D-Calif., chairwoman of the Senate Intelligence committee, said Wednesday that the leak was "within the most serious leaks because it definitely endangered some lives."

Feinstein said it was her understanding that the information gathering did not focus on the "content of phone calls," but rather "to see who reporters have spoken to, that somebody did provide this information with respect to this bomb."

On Wednesday, the leaders of the news organization whose members cover Congress told Cole that "your agency has not provided adequate reason for this disconcerting action."

"We are concerned the incursions by the Justice Department in this case jeopardize the relationship between reporters and anonymous sources, decreasing the likelihood that people will come forward with vital information of public importance," the representatives of the Congressional press galleries said in a letter.

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Associated Press writers Josh Lederman, Erica Werner and Sam Hananel contributed to this report.