If President Barack Obama and congressional Republicans are unable to agree to lift the debt ceiling, Obama could take extraordinary measures that would avoid a crippling government default but would surely invite Republican outrage and likely trigger a constitutional crisis.

Obama is seeking new authority to raise the debt ceiling as part of fiscal cliff negotiations, and he took a hard line Wednesday, saying he would reject GOP efforts to tie new spending cuts to a debt limit increase, as happened last year.

“I want to send a very clear message to people here: We are not going to play that game next year,” Obama said at a White House meeting with business leaders. “I will not play that game. Because we’ve got to break that habit before it starts.”

House Speaker John A. Boehner, R-Ohio, said recently that any increase in the debt limit would come with a “price tag.” Last year, after a showdown that brought the United States to the brink of default, Boehner successfully extracted a dollar in spending cuts for every dollar in additional borrowing capacity, and he has said that demand remains in force.

The White House wants a fiscal cliff deal that boosts the federal government’s borrowing capacity as long as the House and Senate do not muster a veto-proof majority in opposition. Administration officials call it the “McConnell provision,” named for Senate Minority Leader Mitch McConnell, who proposed it as part of the 2011 law (PL 112-25) that raised the debt ceiling. Republicans, including McConnell, rejected the proposal immediately.

Under the administration’s plan, once the president requests an increase in the debt ceiling, Congress would have 15 days to enact a joint resolution of disapproval. If both chambers passed the resolution, it would be sent to the president who could sign or veto it. If the president vetoed the resolution, the government’s borrowing capacity would increase absent a vote to override the veto, requiring two-thirds support in each chamber.

Obama’s drive to take the sting out of the debt ceiling coupled with his forceful language suggest he may reconsider a controversial idea pushed by top Democrats during last summer’s budget negotiations — lifting the debt limit unilaterally, by claiming the 14th Amendment to the Constitution forbids a government default.

Although there is no consensus on the matter, some legal scholars believe the president does have such authority, largely under the 14th Amendment, which states, “the validity of the public debt of the United States … shall not be questioned.”

Neil H. Buchanan, a George Washington University law professor argues the debt ceiling itself is unconstitutional. In addition to its violation of the 14th Amendment, breaching the debt limit would leave the president in a quandary, leaving him to pick whether to defy the law by violating the debt ceiling statute or to ignore spending measures already decreed by Congress.

Buchanan and Michael C. Dorf, a Cornell University law professor, refer to this paradox as the president’s “trilemma” in a legal article.

“The reason the debt ceiling is unconstitutional is the constitutional choice should always be the one that limits the powers of the president,” Buchanan said. “If I were the Republicans, giving the president the authority to pick and choose which spending to cut would scare the bejeesus out of me.”

Not all constitutional scholars share this viewpoint. Lawrence H. Tribe, a constitutional law professor at Harvard, wrote an opinion piece last year arguing the president could not usurp the legislature’s power to borrow money on the credit of the United States.

There’s no question, however, that an executive decree raising the debt ceiling would bring an explosive response from congressional Republicans.

“I don’t think he has the authority to do that,” said Rep. James Lankford, R-Okla. “It does create a constitutional challenge with the courts immediately of what authority does the president have. Does he have unlimited authority to spend?”

GOP leaders also would likely take action to try to halt Obama’s move.

“That would give President Obama, and every future president, authority to spend infinite sums of borrowed money,” said Michael Steel, a Boehner aide. “The American people wouldn’t stand for it, and neither would members of Congress in either political party.”

Buchanan said Republicans could file impeachment charges on Obama and would probably take the president to court. But he said judges might be reluctant to get involved in such a political matter, and that Obama could argue he was simply obeying his oath of office to administer tax and spending programs already approved by Congress.

“I think the president would win on that analysis,” he said.