A congressional panel has heard from government and military whistleblowers who have faced reprisals after speaking out against policies they felt violated the law. One of the witnesses has acknowledged being a source for a New York Times report that revealed the existence of a controversial classified domestic spying program approved by President Bush:

On issues ranging from abuses by some members of the military at Iraq's Abu Ghraib prison, to CIA and FBI counter-terrorism efforts, whistleblowers have played a key role in bringing wrongdoing to the attention of Congress and the public.

They do so at great peril, but Republican Congressman Christopher Shays calls their courage in breaking bureaucratic ranks crucial to helping Congress and the public uncover corruption, fraud and waste:

"Seldom in our history has the need for the whistleblowers unfiltered voice been more urgent, particularly in the realms of national security and intelligence," he said.

Tuesday's five-hour-long hearing heard from five men who allege they faced retaliation.

Samuel Provance, a U.S. Army Intelligence Specialist, who objected to the treatment of prisoners at the Abu Ghraib prison in Iraq said "After what had happened at Abu Ghraib became a matter of public knowledge, and there was a demand for action, young soldiers were scapegoated while superiors misrepresented what had happened and misdirected attention away from what was really going on. I considered all of this conduct to be dishonorable and inconsistent with the traditions of the Army. I was ashamed and embarrassed to be associated with it."

Provance was demoted after refusing what he calls demands by superiors to withhold the truth and support, what he calls, outright lies about Abu Ghraib.

Other testimony came from Lieutenant Colonel Anthony Shaffer, a CIA-trained intelligence officer and Afghanistan war veteran, who was part of a Pentagon program called Able Danger, working to identify terrorists before the September 11, 2001 attacks.

He says superiors tried to silence him, including revoking his government security clearance, after he told the independent September 11 Commission that hijacker Mohamed Atta was identified one year before the attacks:

"I became a whistleblower not out of choice, but out of necessity. The necessity to tell the truth. The commitment to defend this country is not simply going into combat but actually trying to fight the bureaucracy which has slowed us down in many instances," he said.

Appearing for the first time before a public congressional hearing was Russell Tice, a former National Security Agency employee who acknowledged being a source for a New York Times report about a once-secret domestic spying program authorized by President Bush:

"On my way here in here, walking by the Supreme Court, I noticed [the inscription] Equal Justice Under The Law. In the intelligence community, as an intelligence employee, there is no equal justice under the law. Whistleblower protection acts do not apply to us," he said.

Controversy over the program, which involves interception of some communications between individuals in the U.S. and overseas, has led to congressional hearings and criticism from Republicans and Democrats of President Bush's justifications for approving it.

President Bush and others in his administration say U.S. anti-terrorism efforts have been harmed by leaks that helped reveal the existence of the program.

Also testifying was Michael German, a former F.B.I. special agent who resigned to protest what he calls an accepted system of retaliation that hampers anti-terrorism efforts.

Witnesses representing the Pentagon and government agency legal offices sought to explain procedures they follow under laws designed to protect whistleblowers.

"Whistleblowers serve a valuable function in exposing waste, fraud and abuse in government programs and in so doing they deserve protection from retaliation," said Glenn Fine, the Inspector General in the Department of Justice:

Attorney Mark Zaid, who has represented government whistleblowers, says those who risk careers to uncover abuses need to have greater protections:

"It is long overdue that Congress exercises its full weight to create adequate protections for national security whistleblowers, as well as anyone who falls victim to a security clearance process that is rife with abuse," he said.

Lawmakers agreed with Mr. Zaid's argument that changes are needed now more than ever, against the background of efforts by the Bush administration to expand executive power.

Members of Congress appear ready to take legislative steps to strengthen what many see as a broken system of legal protections for individuals vulnerable to reprisals.