WASHINGTON — The Pentagon plans to move up to 10 detainees out of Guantanamo Bay, Cuba, possibly in June, as officials try to reduce the prison’s population before Congress attempts to stop future transfers and derail President Barack Obama’s plan to shutter the U.S. military facility.
In all, the Pentagon hopes that 57 prisoners who are approved for transfer will be resettled by the end of 2015.
That would require “large muscle movements” by at least two countries, which officials hope will each agree to take in 10 to 20 Yemeni detainees who cannot be repatriated because of security conditions in their war-torn homeland.
“I am aware of the clock ticking,” a defense official said, speaking on the condition of anonymity to discuss internal planning. “It’s going to take high-level leadership, and it’s going to take some big asks to some countries.”
Officials said that Defense Secretary Ashton Carter, who has not approved any transfers since he took office in February, will sign off in coming weeks on the repatriation of inmates to Morocco and Mauritania, and the transfer of six Yemeni prisoners to a third country.
Forty-eight of the prisoners approved for transfer out of Guantanamo Bay are Yemeni. The last transfer was in January, when the United States sent four Yemenis to Oman and one to Estonia.
In addition, another prisoner who might be resettled as early as this summer is Shaker Aamer, an accused al-Qaeda plotter and former resident of the United Kingdom whom British officials have long lobbied Washington to release.
The White House faces an increasingly urgent race against time as officials seek to fulfill Obama’s promise to close the detention center, which costs at least $400 million a year and symbolizes for many the mistreatment of terrorism suspects after the Sept. 11, 2001, attacks.
The growing sense of pressure will pose a test for Carter.
The longtime Pentagon official took over responsibility for approving detainee transfers from his predecessor Chuck Hagel, whose reluctance to approve the moves caused friction with the White House before he resigned last year.
Carter, who promised at his confirmation hearing that he would play it “absolutely straight” in assessing Guantanamo Bay inmates, must navigate eagerness at the White House to reduce the prison’s population, worries among many uniformed officers about militants returning to the fight and opposition from many lawmakers to freeing inmates.
The biggest challenge to Obama’s plan lies in Congress, where skeptical lawmakers are moving to tighten restrictions on sending prisoners overseas.
In the Senate, Kelly Ayotte, R-N.H., is sponsoring a bill that would extend the ban on bringing detainees to the United States and would effectively bar future transfers to third countries.
The White House is drafting a plan that officials hope will receive the support of Sen. John McCain, R-Ariz., chairman of the Senate Armed Services Committee, as an alternate to Ayotte’s measure. McCain has previously expressed openness to shutting the prison.
But it’s far from certain, even with McCain’s backing, that lawmakers would fall in behind the White House’s plan, which would allow detainees to be brought to the United States for trial or detention and would enable the continued transfer of others to foreign nations.
In the event that Congress does pass legislation that would freeze Guantanamo Bay’s population at 122, White House officials are exploring options for the unilateral closure of the prison.



