White House staff have been asked to free reporters from any promises of confidentiality they may have made to their sources, US media have reported.
Single-page forms designed to release reporters, if signed, went to Karl Rove, President George Bush's senior political adviser, among other administration officials, Time magazine said on its web site from Friday.
Such a move could be used to force journalists, possibly under the threat of a subpoena, to disclose who revealed that former ambassador Joseph Wilson's wife worked for the CIA.
Wilson has accused Bush aides of compromising his wife's job and safety as an act of revenge after he accused the White House of exaggerating the weapons threat from Iraq, Bush's main justification for going to war last March.
Wilson's accusation, now under investigation, threatens the Bush administration with its biggest political scandal.
Bush adviser Karl Rove denies
he exposed the CIA agent
After his mission to West Africa in early 2002 to investigate US claims that Iraq was trying to obtain uranium for its alleged nuclear weapons programme, Wilson said he told White House officials the allegations were dubious.
But the former ambassador later complained the Bush administration was ignoring his findings, which were backed by the CIA.
When his wife, Valerie Plame, was exposed as a CIA agent by Robert Novak, a rightwing columnist quoting official sources, Wilson said officials were trying to silence him.
Media reports in the US have linked Bush adviser Rove to the CIA leak. When Wilson wrote an editorial criticising the White House, Rove reportedly told MSNBC's Chris Matthews that after Wilson's article, his wife was "fair game".
The White House has denied Rove was responsible for the leak.
Revealing an undercover agent's identity without authorisation is a crime that carries a possible 10-year jail sentence.
The investigation has sparked controversy over whether special legal protections for journalists who keep their sources secret should override the right to punish people for leaks that could compromise national security.
Officials say the FBI must be able
to question reporters involved
NBC News cited unnamed Justice Department officials as saying the FBI could not conduct a thorough inquiry without being able to investigate the reporters involved in the leak.
But experts said a document aimed at releasing reporters from confidentiality agreements would probably have no legal standing.
The reporter-source privilege belongs to the journalist and is not the source's to renounce, Gregg Leslie, legal defence director of Reporters Committee for Freedom of the Press, told Reuters.
On Tuesday, US Attorney General John Ashcroft stepped aside from the politically charged investigation into the leak, taking himself off the case.
The move was seen by some as reducing White House interference in the investigation into whether Bush officials tried to silence Wilson's rejection of their claims about Iraq's nuclear ambitions.
But others have dismissed Ashcroft's move as insufficient, or worse, a ruse.