The Pentagon acknowledged for the first time on Tuesday that all detainees held by the U.S. military, including those at Guantanamo Bay, are entitled to protections under the Geneva Conventions.

The White House announced the policy shift on Tuesday, almost two weeks after a U.S. Supreme Court decision struck down the military tribunal system set up by U.S. President George Bush because it did not obey international law.

The policy, outlined in an internal memo signed by U.S. Deputy Defence Secretary Gordon England, appears to reverse the administration's longstanding position that U.S. detainees are not subject to the international agreements governing the humane treatment of prisoners of war.

Though White House spokesman Tony Snow insisted on Tuesday that all U.S. detainees have been treated humanely, he said, "We want to get it right."

"It's not really a reversal of policy," Snow stressed.

Word of the Bush administration's policy shift came as the Senate Judiciary Committee opened hearings Tuesday on the contentious issue of how detainees should be tried.

"We're not going to give the Department of Defense a blank cheque," Republican Sen. Arlen Specter of Pennsylvania, the committee chairman, told the hearing.

Sen. Patrick Leahy of Vermont, the committee's top Democrat, said "any military commissions "should not be set up as a sham. They should be consistent with a high standard of American justice, worth protecting."

Steven Bradbury, acting assistant attorney general of the Justice Department's Office of Legal Counsel, told the Senate hearing that the Bush administration would abide by the top court's ruling that a provision of the Conventions applies.

But he acknowledged that the provision is vague and hard to interpret.

"The application of common Article 3 will create a degree of uncertainty for those who fight to defend us from terrorist attack," Bradbury said.

Snow said efforts to define detainees' rights will not derail the president's efforts to co-operate with Congress in a bid to proceed with the military tribunals.

The goal is "to find a way to properly do this in a way consistent with national security," Snow said.

The instruction manuals used by the Department of Defense already meet the terms of the humane-treatment provisions of the Conventions' Article 3, Snow said.

They are currently being updated to reflect legislation to more clearly rule out torture.

"The administration intends to work with Congress," Snow said.

"We want to fulfill the mandates of justice, making sure we find a way properly to try people who have been plucked off the battlefields who are not combatants in the traditional sense," he said.

"The Supreme Court pretty much said it's over to you guys (the administration and Congress) to figure out how to do this. And that is where this is headed."

With files from The Associated Press