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 what the administration calls 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 such conditions.

"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 others.

Officials worked intensively on the executive order over the past several weeks, but a senior White House official said that 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 the 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 would effectively force the administration to conduct only military commissions, and, they would be 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 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.

An administration task force ultimately determined that at least 48 detainees were too dangerous to release but could not be put on trial. Officials have said the evidence against these detainees has been tainted by torture or cannot be used in court because it is classified or would not meet legal standards.

"When the review panel puts someone in the category of long-term detention, the 48 people, what happens then?" the administration official said. "Are they there for the rest of their lives? What's the review mechanism? How impartial is it? Do they have a chance to contest it? All of that stuff has to be answered. And we have been working on an executive order laying out these elements."

Those designated for prosecution but who are not charged could also have their cases reviewed under the proposed system in the executive order, the White House official said.

Detainees at Guantanamo would continue to have access to the federal courts to challenge their incarceration under the legal doctrine of habeas corpus. Officials said the plan would give detainees who have lost their habeas petition the prospect of one day ending their time in U.S. custody. And officials said the International Committee of the Red Cross has been urging the administration to create a review process.

Some civil liberties groups oppose any form of indefinite detention, even with a built-in mechanism to challenge incarceration.

"Indefinite detention without charge or trial is wrong, whether it comes from Congress or the president's pen," said Laura W. Murphy, director of the American Civil Liberties Union's Washington legislative office. "Our Constitution requires that we charge and prosecute people who are accused of crimes. You cannot sell an indefinite detention scheme by attaching a few due-process baubles and expect that to restore the rule of law." That is bad for America and is not the form of justice we want other nations to emulate."

The executive order, however, could be an effort to preempt legislation supported by some Republicans, which would create a system of indefinite detention not only for some Guantanamo detainees but also for future terrorism suspects seized overseas.

Malinowski said there is a "big difference" between using an executive order, which can be rescinded, to handle a select group of detainees that Obama inherited, and legislating a general indefinite detention scheme.