WASHINGTON --As lawmakers of both parties continue to question whether the government should close the U.S. military's Guantanamo Bay detention center after reports of prisoner mistreatment, Senate Judiciary Committee Chairman Arlen Specter has called hearings today to clarify the legal rights of those prisoners.

Legal scholars have argued for months over whether detainees at the Guantanamo Naval Base in Cuba should receive the protections afforded to prisoners of war or be classified as "enemy combatants," as the Bush administration has argued, which drastically limits their rights.

Last year, the U.S. Supreme Court ruled that Guantanamo Bay prisoners can challenge their detainment in U.S. courts.

The government responded by setting up military commissions to review the cases. But in November, a U.S. district judge ruled that the new system did not adequately protect the rights of one of the first prisoners moving through the system -- Salim Ahmed Hamdan, an alleged member of the al-Qaida terror network.

That ruling essentially stopped the trials at Guantanamo Bay, but a series of subsequent district court rulings have muddied the issue and were appealed to higher courts.

In the Senate hearing today, Specter intends to explore due process rights of Guantanamo prisoners and the authority that Congress has to ensure that they receive proper legal treatment.

A Specter aide said the Pennsylvania Republican wants to assess whether military tribunals and commissions can provide adequate legal protections for prisoners and to explore ways to create more transparency in the process without jeopardizing national security.

Asked about the issue last week, Specter said congressional oversight of the rights of detainees has been "non-existent" so far. "The Constitution is explicit that this is up to the Congress to legislate on how you handle these issues," he said.

The Judiciary panel's ranking Democrat, Sen. Patrick Leahy of Vermont, said in a speech earlier this week that Guantanamo is "a legal black hole" and "a blot on the conscience of America" and that Congress must step in to create a fair system.

"America was once very rightly viewed as a leader in human rights and the rule of law," Leahy said. "But Guantanamo has drained our leadership, our credibility and the world's good will for America. This is not the American system of justice that I have grown up honoring and appreciating."

Senators have set up two panels for today's hearing. In the first, government officials will testify about the current status of Guantanamo legal battles and explain the system that tries detainees. In the second, several lawyers who have defended detainees will testify about the problems in the process.

At a Pentagon news conference yesterday, Defense Secretary Donald H. Rumsfeld suggested that the Guantanamo prison will be needed for years to come. There is no alternative location to hold and interrogate the suspected terrorists held there, he said.

"I don't know any place where we have infrastructure that's appropriate for that sizable group of people," Rumsfeld said. "The United States government, let alone the U.S. military, does not want to be in the position of holding suspected terrorists any longer than is absolutely necessary, but as long as there remains a need to keep terrorists from striking again, a facility will continue to be needed."

Guantanamo's operations have been more open to scrutiny than any such facility in history, he said.

The approximately 520 prisoners at Guantanamo include terrorist trainers, bomb makers, extremist recruiters and financiers, bodyguards for al-Qaida terror network leader Osama bin Laden and would-be suicide bombers, Rumsfeld said. "They're not common car thieves; they're believed to be determined killers," he said.

The Associated Press contributed to this report. Maeve Reston can be reached at 202-488-3479 or mreston@nationalpress.com.