The bill would authorize temporary transfer of detainees to a U.S. medical facility operated by the Defense Department "to prevent death or significant imminent harm."
Sen. Carl Levin, D-Mich., chairman of the Armed Services Committee, hailed the defense bill provision as a significant change in the long standoff between the Obama administration and bipartisan congressional opponents over the post-Sept. 11 prison for terror suspects.
Levin said the bill has "created a path to close Guantanamo."
The effort still faces resistance from Republicans and Democrats in Congress who have repeatedly and successfully fought White House efforts to move detainees to U.S. soil.
Sen. Jim Inhofe of Oklahoma, the top Republican on the Armed Services Committee, voted for the overall defense bill but is determined to work with his allies in the House to scuttle the provision. Inhofe maintains that Guantanamo is the only option to house terror suspects.
If Obama offers a plan, "I'm hoping that anything that comes can be slow-walked till he's out of office," Inhofe said in an interview Friday.
Another member of the committee, Sen. Kelly Ayotte, R-N.H., said the administration has failed to produce a coherent policy on detention and interrogation, and she promised to lead the Senate effort to keep Guantanamo operating.
"Bringing members of al-Qaida and its affiliates to our homeland and telling them they have a right to remain silent defies common sense, represents a serious national security risk, and prevents us from collecting the intelligence we need to prevent future terrorist attacks and save American lives," Ayotte said in a statement.
Ayotte prevailed in adding another provision to the defense bill a one-year moratorium on transferring detainees from Guantanamo to Yemen, where al-Qaida in the Arabian Peninsula is considered one of the terror group's most dangerous off-shoots worldwide.
Efforts in committee to give the president unfettered authority to close Guantanamo attracted unusual conditions. Sen. Lindsey Graham, R-S.C., won approval for establishing a process in which any administration plan would be subject to a joint resolution of disapproval from both houses of Congress.
The president could veto the resolution, thus requiring a two-thirds majority to override the move.
But even before that, the full Senate must pass the defense bill and that version has to be reconciled with the House legislation, which passed on Thursday. The House bill prohibits any transfer of terror suspects to the United States.
Rep. Adam Smith of Washington state, the top Democrat on the House Armed Services Committee, offered an amendment to close Guantanamo by the end of 2016.
In an appeal for support, Smith described the increasing cost for each detainee $2.7 million per inmate versus about $78,000 for individuals held at maximum security prisons in the United States. He offered the arguments made by Republicans such as former President George W. Bush and onetime Defense Secretary Robert Gates about the need to shutter the facility, with the military saying it undercuts the U.S. fight against al-Qaida and hurts American credibility with its allies.
"We constantly hear the argument that we can't bring terrorists to the United States," Smith said. "The way that argument is stated, it is like we are bringing them here and setting them free. We are not. We are going to lock them up and hold them."
Smith's amendment failed on a vote of 247-177 as 224 Republicans and 23 Democrats opposed it.