The White House revealed to lawmakers on Tuesday details of its request to Congress for a three-year war authority to battle Islamic extremists that would prohibit "enduring" offensive combat operations, AFP reported.
The authorization for use of military force (AUMF) would also allow for use of U.S. special forces, and would not restrict operations to a geographic area, several Democratic senators said after a closed-door briefing by White House officials.
President Barack Obama's team has been deliberating for months on how to move ahead in the next phase of its years-long war against jihadists.
The White House is expected this week to unveil its proposal for authority to combat the Islamic State extremist group, and administration officials have stepped up their deliberations with congressional leaders.
The new AUMF would supersede the open-ended war authority which Congress passed in the aftermath of the 9/11 attacks in 2001. The administration currently uses the 2001 authority to prosecute military action against ISIS, in particular the airstrikes on the group's forces in Iraq and Syria.
Lawmakers have stressed that no official war authority language has been released.
"It was an opening salvo," Senate Democratic leader Harry Reid said after the briefing. "There was nothing finalized yet."
Democratic Senator Robert Menendez said a key plank of the proposal, according to the White House briefers, required "no enduring offensive combat" operations, a qualifier he acknowledged could face opposition in Congress.
"Unless that is further defined, that might be seen as too big a statement to ultimately embrace because, forget about Barack Obama, there would be a new president in two years," Menendez said, according to AFP.
"The challenge to get a broad bipartisan AUMF is threading the needle between not having too expansive an authorization that can be used for an open-ended, prolonged conflict, and however giving an authorization that gives the president the wherewithal to effectively defeat ISIL," he added, using another name for the terrorist group that has seized swathes of territory in Iraq and Syria.
Senator Dianne Feinstein said she understood that the request for a three-year authorization would allow for special operations.
But "I think the big discussion will be over how you word the language on troops," the top Democrat on the Senate Intelligence Committee said.
Some Republicans were already pushing back.
"I will agree to nothing that restricts the president's latitude of action," hawkish Senator John McCain told reporters.
Language barring enduring combat operations "would be unacceptable to me," he said, adding that any debate about the war authority should not be rushed.
Republican Senator Lindsey Graham said he was briefed by the White House by phone and was disturbed that the new authority would not allow U.S. forces to protect American-trained Syrian rebels against air attacks by strongman Bashar Al-Assad's military.
"I'll be a no to that," he declared.
ISIS has taken advantage of the Syrian civil war and instability in Iraq to seize chunks of territory in the two countries, where it has committed atrocities that the UN has denounced as crimes against humanity.
A U.S.-led coalition which includes Arab and other Western countries, has targeted its positions with air strikes since September.
Secretary of State John Kerry said on Sunday that the assault against ISIS was beginning to win back territory and deprive the jihadists of key funds.
The air war had helped to retake some 700 square kilometers (270 square miles) of territory, or "one-fifth of the area they had in their control", he said.
Kerry added the coalition had "deprived the militants of the use of 200 oil and gas facilities… disrupted their command structure… squeezed its finance and dispersed its personnel."
Later on Sunday, top U.S. envoy John Allen said that Iraqi forces will begin a ground offensive "in the weeks ahead" to take back swathes of the country seized by ISIS.
"There will be a major counter offensive on the ground in Iraq," he said in an interview with Jordan's official Petra news agency.
"In the weeks ahead, when the Iraqi forces begin the ground campaign to take back Iraq, the coalition will provide major firepower associated with that," he added, stressing that the Iraqis would lead the offensive.
AFP contributed to this report.