WASHINGTON -- He's the dean of Duquesne University Law School. But on Sept. 11, 2001, retired Navy Rear Admiral Donald J. Guter was on the frontline in America's war on terrorism.

"I was in the Pentagon on 9/11," Mr. Guter, the former chief judge advocate general, or JAG, of the Navy, told a Senate panel yesterday. "I lost one of my lawyers in the airplane that came back and hit the Pentagon that day, and I've lost friends since then. So I'm no stranger to the struggle that we face."

Yet he's also a major critic of the Bush administration's denial of habeas corpus rights for terrorism suspects held at Guantanamo Bay, Cuba, and elsewhere.

In a Senate Judiciary Committee hearing, he added his voice to a sizeable group of legal and military experts who warn that such policies violate the U.S. Constitution and are hurting the nation's moral standing in the world.

"Habeas corpus is the basis for a civilized legal system. It protects us against an unchecked power to hold people indefinitely," Mr. Guter said. "And now it pains me to say that we lead the charge in trying to destroy it."

Last year, President Bush signed the Military Commissions Act of 2006, which prevents detainees who aren't U.S. citizens from challenging their detentions in civilian courts.

Administration officials warned that terrorism suspects would flood the courts with habeas petitions, slowing the progress of prosecutions. They argued that secret military tribunals were the best way to handle the detainees and protect national security.

Pennsylvania's Sen. Arlen Specter, the ranking Republican on the Judiciary Committee, tried unsuccessfully to amend the legislation in October, although he voted for its final version.

Now he and committee Chairman Patrick Leahy, D-Vt., are leading a congressional effort to reinstate habeas corpus rights.

Mr. Specter said several key Supreme Court decisions demonstrated that suspects held at Guantanamo have the right to challenge their detentions. But he expressed surprise that the high court last month declined to take up a new case aimed at the constitutionality of the military commission law.

"When you say we're going to restore the great writ [of habeas corpus], the great writ doesn't need to be restored," he said. "It was always here. It's just a question of recommending its application in Guantanamo."

Mr. Guter eagerly agreed.

"For me this issue is about what is best for the long-term policy for the United States, what is best for our troops, and what is best for our citizens who travel overseas," he said. "What gives us the best chance of winning the hearts and minds of the people around the world? What policy serves the rule of law?"

A native of Latrobe who graduated from Duquesne Law School in 1977, Mr. Guter spent two decades in the Navy's legal branches. In 2000, he became the head of the JAG Corps.

During the Sept. 11 terrorist attacks, former JAG attorney Mari-Rae Sopper was aboard American Airlines Flight 77, which struck the Pentagon. Mr. Guter described her funeral as a dark moment for him.

In the months after the attacks, he was one of several military officials who recommended the U.S. naval base at Guantanamo Bay as a possible location to hold detainees.

Mr. Guter retired from the Navy in 2002. He soon joined other Guantanamo critics in filing friend-of-the-court briefs on behalf of detainees. Yesterday was his first appearance before Congress.

David B. Rivkin, a Washington lawyer and a fellow at the Nixon Center, defended the constitutionality of the government's detention process for suspects during yesterday's hearing. He argued that U.S. military tribunals are less strict than guidelines outlined in the Geneva Convention, allowing an annual review of a detainee's status.