US Defense Secretary Robert Gates has ordered plans to be drafted for the closure of the Guantanamo Bay detention centre, the Pentagon says.
A team was looking at moving inmates from the facility in a way that continued to protect the American people, a spokesman said.
About 250 detainees remain in the controversial Cuba camp.
US President-elect Barack Obama says closing the camp “in a responsible way” is one of his top priorities.
Mr Obama, who takes office on 20 January, said earlier this week he aimed to close the facility within two years.
Pentagon spokesman Geoff Morrell said Mr Gates – who is to retain his position in the new administration – had wanted to be prepared in case Mr Obama wished to tackle the issue “early in his tenure”.
“He has asked his team for a proposal on how to shut it down, what will be required specifically to close it and move the detainees from that facility, and at the same time protect the American people from dangerous terrorists,” he said.
New legal process
The Guantanamo Bay prison opened shortly after the attacks of 11 September 2001. Hundreds of men suspected of links to terrorism or al-Qaeda were held without trial as “unlawful enemy combatants”.
Many are now challenging their detention in civilian courts, after a ruling in June by the US Supreme Court.
Some officials have warned that closing the camp would be an extremely complicated process.
Those still detained there include men alleged to have planned the 9/11 attacks.
How and where they would be detained or tried in the future simply is not clear, reports the BBC’s Adam Brookes from Washington.
The incoming president, the Department of Justice and perhaps Congress will need to build a whole new legal process for handling the remaining Guantanamo detainees, our correspondent says.