WASHINGTON - The US Senate on Thursday is expected to open the way for President Barack Obama to speed up the transfer of many prisoners from Guantanamo Bay to their home countries, a crucial step toward the long-delayed closure of the military prison.

Tucked inside a defense spending bill awaiting final congressional approval, a bipartisan deal will ease some of the tough restrictions on Obama's ability to send more of the 158 remaining inmates home after years of detention without trial at the US Naval Base in Cuba.

Even with the new legislation, Obama will still face major obstacles to shutting Guantanamo. But he will be in a better position than before to reduce the detainee population at the facility, which has long been the object of international condemnation.

"While the bill does not address all of the administration's concerns, its provisions regarding foreign transfers of detainees ... will provide the administration additional flexibility to transfer detainees abroad consistent with our national security interests," White House spokesman Jay Carney said.

Obama repeatedly pledged to close Guantanamo when he was campaigning for a first term and after he took office in 2009. But he blamed congressional resistance for frustrating his efforts to vacate the camp, which was opened by his predecessor, George W. Bush, to hold terrorism suspects rounded up overseas after the September 11, 2001 attacks.

Renewing his long-standing vow to shutter the prison in a major policy speech at Washington's National Defense University in May, Obama called it "a symbol around the world for an America that flouts the rule of law."

The administration then named two special envoys to oversee the effort, stepped up negotiations with other countries, including Saudi Arabia, Algeria and Yemen, and worked with Congress to craft a compromise deal.

Ban on Transfers to US to Remain Infact

Though lawmakers on both sides of the aisle refused to budge on a ban on bringing Guantanamo prisoners to the US mainland, they gave ground on the rules for sending prisoners home.

Among the earlier restrictions was that the administration had to certify that the country where an inmate was being sent was not "facing a threat that is likely to substantially affect its ability to exercise control over the individual." This all but ruled out politically chaotic Yemen, home to the largest group of Guantanamo detainees.

Transfers were also banned to countries that Washington had designated "state sponsors of terrorism," a category that made it difficult to move Syrian inmates. Prisoners also could not be sent back to any country where previously released Guantanamo detainees had returned to "terrorist activity."

Such rules were lifted or significantly relaxed under the current bill, the National Defense Authorization Act, which was approved by the House of Representatives last week.

Even before the Senate gave final congressional approval, the administration had been showing signs of a more active transfer policy. In recent weeks, it sent two detainees back to Sudan, two to Saudi Arabia and two to Algeria.

About half of Guantanamo's remaining detainees have been cleared for transfer or release since 2009, but most were blocked from going home because of congressional restrictions.

While more transfers are sure to follow, the White House made clear that it will move carefully. Obama can also expect continued pressure from some lawmakers, including Republican critics, who want to keep Guantanamo open.

"The president has directed the administration to responsibly reduce the detainee population to the greatest extent possible," said National Security Council spokeswoman Caitlin Hayden.

"Even in the absence of transfer restrictions, our longstanding policy is to transfer detainees only if the threat posed by the detainee can be sufficiently mitigated and when consistent with our humane treatment policy," she said.

On top of that, complications remain with Yemen, where an active al Qaida branch is the main US concern. The Yemeni government also has yet to build a long-promised detention center to house any Guantanamo prisoners sent home.