The White House backed legislation to strengthen journalists' rights to protect sources on Wednesday, amid a growing firestorm over the government's seizure of reporters' phone logs.

President Barack Obama urged lawmakers to pass a so-called media shield bill, his spokesman said, as criticism grew over the secret collection of the telephone records of the Associated Press.

"The president has long supported media shield legislation in the Senate, during the 2008 campaign, and as president," White House spokesman Jay Carney said, adding that Obama had spoken to Senator Charles Schumer, who reintroduced his shield proposal.

Schumer said his bill would require prosecutors to convince a judge that information being sought would "prevent or mitigate an act of terrorism or harm to national security."

The senior lawmaker said the law "would balance national security needs against the public's right to the free flow of information."

The American Civil Liberties Union praised the move to revive the shield law, which failed in prior legislative efforts.

"The White House deserves credit, they should be commended for taking a proactive approach, but they should ensure that any bill that actually goes to the president's desk would effectively prevent what happened here," ACLU counsel Gabe Rottman said.

Ken Paulson, a former USA Today editor who heads the First Amendment Center, also backed the idea.

"We've seen a lot of outraged quotes from members of Congress," he said.

"It would be terrific if they could channel that outrage into ensuring greater protection for a free press."

After the AP revealed the subpoenas on Monday, commentators and media organizations accused Obama's administration of trampling on press freedoms in its pursuit of government leaks and whistleblowers.

More than 50 media organizations protested the government seizure, in a letter released by the Reporters Committee for Freedom of the Press.

The coalition said the seizure "calls into question the very integrity of Department of Justice policies toward the press and its ability to balance... its police powers against the (constitutional) First Amendment rights of the news media and the public's interest."

Attorney General Eric Holder defended the action Tuesday, saying it was part of a probe into a security breach which had put "the American people at risk."

"That's not hyperbole," he insisted.

Facing questions from lawmakers on Wednesday, Holder said, "The case is really not about the AP, it's about the people who leaked."

He also backed the Schumer proposal, saying: "There should be a shield law with regard to the press's ability to the gather information and to disseminate it... the focus should be on those people who break their oaths and put the American people at risk, not reporters who gather this information."

Criticism from news organizations meanwhile increased on Wednesday.

The Washington Post said in an editorial that "whatever national security enhancement this was intended to achieve seems likely to be outweighed by the damage to press freedom and governmental transparency."

New York Times public editor Margaret Sullivan said in a column: "This was supposed to be the administration of unprecedented transparency

"Instead, it's turning out to be the administration of unprecedented secrecy and of unprecedented attacks on a free press."

Al Tompkins of the Poynter Institute, a media education group, said that the government's ability to seize the logs despite free press protections "reminds me of the fact that North Korea's government has a statute on the books promising a free press.... the Justice Department's guidelines, like North Korea's free-press law, proved worthless as soon as they proved untidy."

Separately, The New Yorker magazine unveiled a new online system for anonymous whistleblower tips, based on technology developed by the late Internet activist Aaron Swartz and a former hacker.

Senior editor Amy Davidson said that under the "Strongbox" system "even we won't be able to figure out where files sent to us come from. If anyone asks us, we won't be able to tell them."

The system aims to encourage the anonymous submission of newsworthy information, in the manner of WikiLeaks and other Internet sites. The Wall Street Journal set up its own tip system in May 2011 called SafeHouse.

-- --

[Spying on computer via Shutterstock]