The specter of another Washington leak investigation has been raised in the wake of December's revelation that President Bush authorized the National Security Agency to monitor phone calls and e-mails inside the United States without court warrants.

But unlike the ongoing leak investigation into who identified a CIA operative, it's not yet clear if such an investigation would be legal, says at least one observer.

"The government has no legal right to pursue the whistleblower [or] whistleblowers who disclosed what's been publicly aired to date," Tom Devine, the legal director for the Government Accountability Project and a lawyer who represents whistleblowers, told FOXNews.com.

The New York Times was first to report on Dec. 16 that without judicial approval, the NSA has been monitoring phone calls and e-mails in which one party to the conversation was inside the United States. The warrantless wiretaps allegedly fly in the face of standing federal surveillance law.

The day after the report broke, Bush acknowledged that he had authorized the program, saying it only focused on members or associates of Al Qaeda. He added that the Constitution and congressional resolution permitted his decision, which was necessary because the 1978 Foreign Intelligence Surveillance Act doesn't allow U.S. intelligence to act quickly enough.

The president has also described the leak as "shameful," saying the program's disclosure gives terrorists the upper hand. He said he presumed the Justice Department would look into the matter if the NSA requests a probe of the leak.

Pressed by reporters about whether a leak probe would be started, Attorney General Alberto Gonzales wouldn't commit to it, but wouldn't rule it out, either.

"We'll just have to wait and see," Gonzales said.

Several lawmakers have demanded hearings into the NSA surveillance while others have also said the leak itself is a serious breach.

Sen. Jay Rockefeller, D-W.Va., vice chairman of the Senate Intelligence Committee and one of the members briefed by the administration about the surveillance plan, expressed deep reservations about the program to the vice president in 2003. But he said he also would like hearings into who leaked the story to reporters at the Times.

Reps. Peter Hoekstra and Jane Harman, the chairman and ranking Democrat, respectively, on the House Intelligence Committee, also condemned the leak, saying it hurt national security.

While Harman, of California, said she believes broader oversight is needed of the NSA program, "its disclosure has damaged critical intelligence capabilities."

"These politically motivated leaks must stop," Hoekstra, of Michigan, said in a statement.

A possible leak investigation could take at least two forms: through normal channels within the Justice Department or through a special task force. The investigation could focus on individuals in the media or the government.

Ronald Cass, a legal scholar and former dean of the Boston University School of Law, told FOX News that special investigations can be distractions, and too much pressure will be put on bringing back an indictment.

"It's better to leave these matters in the hands of the Justice Department; let them handle it through the ordinary course," Cass said.

But a special prosecution might be needed to speed up the process, said Edward Turzanski, a senior fellow of the Foreign Policy Research Institute and a national security analyst at La Salle University.

"We've reached a critical mass," Turzanski told FOX News. "There's too much damage to our national security capabilities, to critical information and to the war-fighting effort. And that is where this urgency comes in," Turzanski said.

Devine said at least two laws protect a potential leak source. One is a so-called anti-gag statute that prevents the government from spending money on a leak investigation unless it specifically warned the employee that its gag rules cannot trump good-government laws.

The leak also could be legal if the Whistleblower Protection Act covers it, Devine said, as long as the leaker was not in the FBI, CIA or NSA, which aren't covered by the act. For instance, a civilian Pentagon employee who wanted to expose government wrongdoing would have free speech protections to expose abuses of power or illegal actions.

The laws don't apply to public disclosure of classified information, Devine said, but a government worker could tell an inspector general if wrong-doing involving classified information has occurred. Because it's not yet known if classified information was given to reporters, there's no telling yet if that's a problem in this case.

So far, though, Devine said he thinks everything he's seen published so far is safe from prosecution. "This has been apple pie, protected speech," he said.

Tom Rosenstiel, director of the Washington-based Project for Excellence in Journalism, told FOXNews.com undoubtedly the Times story was enabled by a leak. But noting the ongoing investigation into the leak of CIA operative Valerie Plame Wilson's identity, he said politicians will have a hard time meeting the burden of proof of criminality in a leak.

"There's a difference between a leak that violates, or might violate a specific law against outing an individual who's undercover or whose identity is classified, and an investigation into the more general kind of leaking about operations policies, that goes on, frankly, every day in this town," Rosenstiel said.

Because of that, Washington's press corp doesn't appear to be greatly concerned. But Rosenstiel said it doesn't mean journalists should forget about the ethics of revealing secretive or sensitive information.

Rosenstiel stopped short of saying whether the Times should have run the story; rather, he said, those decisions are made on a case-by-case basis that changes not only by the story but by the people running the newsroom. The Times has said it held the story for a year after the administration told editors it could harm national security

"There is no perfect equation," Rosenstiel said. "We want journalists to be parsing out and not just publishing everything they take in. ... If you're just putting everything you know in the newspaper ... then you're not doing your job."

Georgetown University constitutional law professor Peter Rubin said he hasn’t seen anything in the stories that gives terrorists additional information about government operations. It’s widely known, he said, that the United States can spy on people via wiretaps without letting the subject of the wiretap know beforehand — that’s the purpose of the Foreign Intelligence Surveillance Court, created under the Foreign Intelligence Surveillance Act.

Rubin said a leak investigation shouldn’t be ruled out, because illegally putting out classified information is still a crime. But regardless of whether a leak investigation continues or not, he said he thinks that the general public is better off now than it was before the story about domestic spying broke.

“It seems obvious that they’re better off by having this story in front of them,” Rubin said.

He said the NSA program is “a dramatic step of spying on American citizens in the United States. I think most people were very surprised to hear it,” including lawmakers on both sides of the aisle.

“That suggests a level of gravity of this,” Rubin said. The government has not said who has been the subject of eavesdropping, but that it may have involved American citizens.

The New York Times reported that the eavesdropping program helped uncover a plot by Iyman Faris, an Ohio trucker and naturalized citizen who pleaded guilty in 2003 to helping Al Qaeda plan to blow up the Brooklyn Bridge in New York.

If a leak investigation should open into the NSA domestic spying program, it wouldn't be the first time and certainly won't be the last.

The Plame investigation has resulted in an indictment of former vice presidential chief of staff I. Lewis "Scooter" Libby on obstruction charges. Libby resigned, but prosecutor Patrick Fitzgerald has called for a new grand jury and continues to focus on presidential adviser Karl Rove's activities.

In the Plame case, syndicated columnist Robert Novak first published Plame's identity, but he has been quiet on who his sources were. Although Novak has not been called in to testify before a grand jury, he is believed to be cooperating in the investigation. No one has been charged in the actual commission of a crime related to the leak.

In another story published in November, The Washington Post revealed the existence of secret "black site" prisons run by the CIA in a handful of countries, including in Eastern Europe. That story has been referred to the Justice Department, and lawmakers also have planned hearings into the matter.