Some 650 prisoners held by the US at Guantanamo Bay are now to have their detentions reviewed once a year.
US Defence Secretary Donald Rumsfeld said new panels would determine whether inmates remained a threat to America.
But he again defended the continued detention of the prisoners without charges as “a security necessity”.
Mr Rumsfeld’s comments came as a Spanish detainee was transferred from Guantanamo Bay in Cuba to Spain in the first such release of its kind.
Abderrahman Ahmad – captured in Afghanistan in 2001 – now faces questioning about his alleged involvement with a Spanish al-Qaeda cell.
Mr Ahmad, 29, is one of four Guantanamo inmates to be charged by Spanish High Court Judge Baltasar Garzon with having links to the al-Qaeda cell discovered in November 2001.
The maximum-security prison at Guantanamo Bay holds suspected al-Qaeda and Taleban fighters from more than 40 countries captured in Afghanistan and elsewhere.
Human rights groups and some foreign governments have criticised the detainees’ treatment and the lack of trials or access to lawyers.
The US insists that they are “illegal combatants”, not prisoners of war, and can if necessary be tried by military tribunals.
A Pentagon spokesman said the new three-member panels would include intelligence analysts and people who had interrogated prisoners.
Sarah Green, Amnesty International
Asked if the prisoners would be allowed legal representation when going before panels, he said precise details of how they would operate had yet to be finalised.
But he added that prisoners would be allowed “some form of representation”.
Defence of policy
BBC Pentagon correspondent Nick Childs says the announcement of the review panels is a tacit acknowledgement that many of those detained at Guantanamo Bay could be there for a long time.
He adds that it was announced during a speech which amounted to the most comprehensive public defence of the detentions by a senior Bush administration official.
Mr Rumsfeld insisted the policy was consistent with the international laws of war.
“I recognise that in our society the idea of detaining people without lawyers seems unusual, detaining people without trial seems unusual,” he told the Greater Miami Chamber of Commerce.
“We need to keep in mind that the people in US custody are not there because they stole a car or robbed a bank.
“They are enemy combatants and terrorists who are being detained for acts of war against our country and that is why different rules have to apply.”
However, those considered to pose no threat to America would be released, Mr Rumsfeld said.
US officials say the lengthy detentions were vital to intelligence-gathering, and that information obtained from prisoners at Guantanamo Bay has led to arrests around the world.
The BBC’s Matt Frei in Washington said he had spoken to a lawyer representing British prisoners who indicated the cases of Britons and Australians were on hold.
This was in direct contradiction to what the US Department of Defense had said, insisting they would hasten the release of those people they no longer deem to be a threat.