The Obama administration is preparing an executive order that would formalize indefinite detention without trial for some detainees at the U.S. military prison at Guantanamo Bay, Cuba, but allow those detainees and their lawyers to challenge the basis for continued incarceration, U.S. officials said.

The administration has long signaled that the use of prolonged detention, preferably at a facility in the United States, was one element of its plan to close Guantanamo. An interagency task force found that 48 of the 174 detainees remaining at the facility would have to be held in what the administration calls prolonged detention.

"We have a plan to close Guantanamo, and this detainee review process is one element," said an administration official who discussed the order on the condition of anonymity because it has yet to reach the president.

However, almost every part of the administration's plan to close Guantanamo is on hold, and it could be crippled this week if Congress bans the transfer of detainees to the United States for trial and sets up steep hurdles to the repatriation or resettlement in third countries of other detainees.

Officials worked intensively on the executive order over the past several weeks, but a senior White House official said it had been in the works for more than a year. If Congress blocks the administration's ability to put detainees on trial or transfer them out of Guantanamo, the official said, the executive order could still be implemented.

"I would argue that you still have to go ahead because you can't simply have people confined to a life sentence without any review and then fight another day with Congress," the administration official said. "One of things we're mindful of is [that] you can't have a review conducted by the same people, in the same process, who made the original decision to detain. You have to have something that is different and is more adversarial, which the Bush administration never had."

Under the system established by the previous administration, Guantanamo detainees could go before military review panels with "personal representatives," also military officers, who explained the process but could not act as lawyers. The system envisioned under the executive order would be more adversarial and would allow detainees to challenge their incarceration periodically, possibly every year.

"There isn't a single serious commentator on the subject who hasn't thought something like this wasn't necessary as part of a rule-of-law approach," said the senior White House official, who also spoke on the condition of anonymity.

Provisions in the defense authorization bill, which has passed the House and is before the Senate, would effectively ban the transfer of any detainee to the United States for any purpose. That rules out civilian trials for all Guantanamo detainees, including Khalid Sheik Mohammed, the self-proclaimed mastermind of the Sept. 11, 2001, attacks. His potential prosecution had remained possible even though the administration had balked in the face of political opposition to a trial in New York.

The defense bill, if it passes the Senate, would effectively force the administration to conduct only military commissions and at Guantanamo Bay, which would also have to remain open to house those held indefinitely. The bill would also create new requirements before the administration could repatriate or resettle detainees who were cleared for release by the interagency task force.

"If it passes, it is the final, decisive blow to the president's plan," said Tom Malinowski, head of the Washington office of Human Rights Watch.

In a speech at the National Archives in May 2009, President Obama said his administration would use criminal trials, reformed military commissions, transfers to other countries, releases and continued detention in pursuit of its commitment to close Guantanamo.