The White House threatened on Tuesday to veto emergency legislation pending in the House to avert a threatened national default, a pre-emptive strike issued as Republican Speaker John Boehner laboured to line up enough votes to pass the measure.

Mr. Boehner faced criticism from some conservatives in advance of an expected vote on Wednesday.

The bill would raise the debt limit by $1 trillion while making cuts to federal spending of $1.2 trillion — reductions that conservatives say aren’t enough.

The measure also would establish a committee of lawmakers to recommend additional budget savings of $1.8 trillion, which would trigger an additional $1.6 trillion increase in the debt limit.

The White House objects to the requirement for a second vote before the 2012 elections.

Majority Leader Harry Reid said the measure stood no chance of passing the Senate even if it clears the House. He pronounced it “dead on arrival.”

Washington and the nation are staring down an Aug. 2 deadline to raise the debt limit or face national default

The political and financial crisis gripping the U.S. appeared Tuesday to have deepened after President Barack Obama and House Speaker John Boehner accused one another in nationally televised speeches of failing to negotiate in good faith to avert an unprecedented and catastrophic American default early next week.

Neither of the rival plans offered by Mr. Boehner in the House and Mr. Reid in the Senate seemed to have the necessary votes in Congress amid a bitter stalemate that could have far-reaching repercussions for the fragile U.S. economy as well as global markets. Stocks fell Tuesday as U.S. markets registered their nervousness over the Washington gridlock between Obama and Republicans.

At the White House, spokesman Jay Carney said the administration remains in contact with congressional leaders despite the collapse of talks last Friday and inconclusive discussions this past weekend.

“We’re working on Plan B. … There has to be a product that can pass the House and the Senate and be signed into law,” said Mr. Carney, who also argued that the Boehner plan had no chance of passing in the Senate.

Mr. Carney insisted that Aug. 2 is the drop-dead date for the Treasury’s cash flow — “beyond that date we lose our capacity to borrow” — and expressed confidence that the debt ceiling would be raised by the deadline.

The continued bickering on Capitol Hill overshadowed any signs of emerging common ground.

An influential conservative advocacy group urged lawmakers to vote against both plans. “Speaker Boehner’s most recent proposal to raise the debt limit is regrettably insufficient to our times,” Heritage Action for America said in a letter Tuesday to House members.

Still, Mr. Boehner told reporters that the “we are going to have some work to do to get it passed, but I think we can do it.”

In the Senate, Mr. Reid challenged Republicans to back his competing legislation, arguing that the no-taxes, government-cuts proposal was just what they wanted.

“In short, it’s everything the Republicans have demanded wrapped up in a bow and delivered to their door,” Mr. Reid said at the start of the Senate session.

In a prime-time address Monday night, Mr. Obama pleaded for compromise and urged Americans to contact their lawmakers.

“We can’t allow the American people to become collateral damage to Washington’s political warfare,” Obama told the nation.

Mr. Boehner, in a rebuttal, said he had given “my all” to work out a deal with Mr. Obama.

“The president would not take yes for an answer,” he said.

Congressional officials said the House switchboard was near capacity with a high volume of calls and suggested using backup numbers. Websites also experienced heavy traffic, and lawmakers were sending out appeals for patience. Unclear was whether the callers echoed Mr. Obama’s argument or backed Mr. Boehner’s call for his approach.

In afternoon trading on Wall Street, stocks were mixed as the financial markets warily watched the standoff.