WASHINGTON » President Barack Obama’s formal request for congressional authorization to fight the Islamic State — once framed by lawmakers as a matter of great constitutional import — is now seriously imperiled because Republicans think it does too little and Democrats think it does too much.

And neither the White House nor many members of Congress seemed in any rush to bridge the divide.

Secretary of State John Kerry and other top administration officials urged members of the Senate Foreign Relations Committee on Wednesday to approve Obama’s request, but it was clear during the contentious three-hour session that lawmakers were far from reaching any agreement.

When Obama, in his news conference after the midterm elections in November, announced he would seek specific authorization from Congress, he said, "The world needs to know we are united behind this effort." But there is little evidence that after the proposal went to Congress, the administration lobbied members to win support for its request, and few suggestions that Democratic and Republican lawmakers are successfully working toward an alternative.

Despite urging Congress to pass the authorization for military action, Kerry, Defense Secretary Ash Carter and Gen. Martin E. Dempsey, chairman of the Joint Chiefs of Staff, all made clear that they believe the administration already has the legal authority to pursue its military campaign against the Islamic State under two previous authorizations: one in 2001 allowing the president to fight a global war against al-Qaida and its affiliates, and one in 2002 that enabled President George W. Bush to wage war in Iraq.

"The president already has statutory authority to act against ISIL," Kerry said, referring to the Islamic State, which is also known as ISIS. "But a clear and formal expression of this Congress’ backing at this moment in time would dispel doubts that might exist anywhere that Americans are united in this effort."

Kerry also called on Congress to speak "with a single powerful voice at this pivotal hour."

But given that military operations have been underway for months, the White House views the resolution as symbolically important but not required.

Sen. Rand Paul, R-Ky., a member of the committee and a likely 2016 presidential hopeful, expressed frustration with the administration’s willingness to continue its military campaign with or without congressional authorization.

"It’s disdainful to say, ‘Well, you know, we want y’all to pass something, but it doesn’t really matter because we’ll just use 2001,’ which is just absurd," Paul said. "And it just means that Congress is inconsequential."

For now, the legislation appeared to be faltering under the collective weight of lawmakers who all remain wary, but for very different reasons. Democrats worry that the authorization allows the country to embroil itself in another endless conflict overseas, while Republicans say it unnecessarily limits the president’s ability to fight the Islamic State effectively, including the potential for U.S. ground troops.

Sen. Bob Corker, R-Tenn., the chairman of the committee, said he did not know of "a single Democrat" who supports the administration’s current request, and he warned, "What that does on this side of the aisle is put Republican senators in the position of looking at a limited authorization for the use of military force that, in some ways, ratifies a strategy, especially in Syria, that many people do not believe is effective."

Earlier in the week, Corker warned, "One of the things we don’t want to do is embark on a plan that leads nowhere."

But the rationale for the Democrats’ position is completely opposite that of the Republicans.

Sen. Robert Menendez of New Jersey, the top Democrat on the committee, said his party was not willing to give the president "a blank check" or "an open-ended authorization for war."

The White House’s proposed legislation would prohibit the use of "enduring offensive ground combat operations" and limit the engagement to three years, an approach that Carter said was a "sensible and principled provision." It would also repeal Congress’ 2002 authorization of force, while leaving in place the 2001 measure.

"I cannot tell you that our campaign to defeat ISIL would be completed in three years," Carter said. But, he added, "the president’s proposed authorization affords the American people the chance to assess our progress in three years’ time and provides the next president and the next Congress the opportunity to reauthorize it, if they find it necessary."

The debate over military action has been further complicated by partisan friction over the administration’s negotiations to freeze Iran’s nuclear program in exchange for the lifting of some sanctions, an effort that many Republicans strongly oppose.

Sen. Marco Rubio, R-Fla., also a likely 2016 presidential hopeful, said he believes that "much of our strategy with regards to ISIS is being driven by a desire not to upset Iran so that they don’t walk away from the negotiating table on the deal that you’re working on."

"Tell me why I’m wrong," Rubio pressed Kerry.

"Because the facts completely contradict that," Kerry replied.

Kerry, at the urging of a Democratic senator, also criticized a recent open letter to Iran’s leadership that warned about any nuclear agreement, calling it "quite stunning." The letter was drafted by Sen. Tom Cotton, R-Ark., and signed by 47 Republicans.

"My reaction to the letter was utter disbelief," Kerry said.

Paul, who signed the letter, made a point of telling the administration officials that "the letter was to you."

"The letter was to Iran, but it should’ve been CC’d to the White House because the White House needs to understand that any agreement that removes or changes legislation will have to be passed by us," Paul said.

After the hearing, Sen. Tim Kaine, D-Va., said that although he did not like the language the administration had sent over, he would reserve judgment until a final proposal came out of the committee, and that he remained modestly optimistic.

"Bottom line, a strong supermajority of both houses supports U.S. military action against ISIL," Kaine said. "That doesn’t mean the details and the differences aren’t important, but start with that proposition, that there’s strong bipartisan support for military action."

Now, he added, "we’ve just got to figure out a way to express it."

© 2015 The New York Times Company