One hour before they had hoped to present a plan, Democratic and Republican leaders said were still unable to reach a compromise that would stop the automatic tax hikes and spending cuts that could push the economy into recession.
"There are still serious differences between the two sides," Senate Democratic Leader Harry Reid said.
A sticking point appeared to be a Republican proposal, floated late on Saturday (local time), which would slow the growth of Social Security retirement benefits in an effort to narrow trillion-dollar budget deficits. Many Democrats, including Reid, have said Social Security should not be touched.
With negotiations at an apparent standstill on Capitol Hill, Senate Republican Leader Mitch McConnell said he would now try to hammer out an agreement with Vice President Joe Biden.
"I'm willing to get this done, but I need a dance partner," McConnell said.
Any agreement needs to be rushed through both chambers of Congress before midnight on Monday. Even if the two sides reach an agreement, procedural barriers in the Senate and the House of Representatives make quick action difficult.
If the politicians cannot agree, then tax increases and across-the-board government spending cuts will begin on January 1. That would take $US600 billion out of the economy, push unemployment up and curb federal spending.
Another major disagreement was over tax hikes on the wealthy, an increase sought by President Barack Obama but opposed by Republicans, particularly fiscal conservatives in the House of Representatives.
Republicans aim to pair any tax increase with spending cuts to benefit programmess that are projected to grow ever more expensive as the population ages in coming decades.
But their proposal to slow the growth of Social Security benefits by changing the way they are measured against inflation met fierce resistance from Democrats. Obama included the proposal, known as "chained CPI," in an earlier proposal, but many of his fellow Democrats remain opposed.
"We consider it a poison pill - they know we can't accept it. It is a big step back from where we were on Friday," a Senate Democratic aide said.
Obama made a rare appearance on NBC's Meet the Press to pressure lawmakers into forging a deal.
Senators appearing on other Sunday morning shows expressed optimism that an agreement could be reached.
Republican Senator Lindsey Graham conceded that an agreement would end up raising income taxes on the wealthy, thus sparing the rest of the country from the looming income tax hikes.
"President Obama is going to get tax rate increases. The president won," Graham tweeted, echoing earlier comments he made on Fox News Sunday. He told the show that the chances of a bipartisan deal before the New Year's deadline were "exceedingly good."
Obama has alternatively offered Republicans a deal to increase income taxes for households earning over $US250,000 a year, and over $US400,000 a year.
A White House aide said the president and his staff had been in touch with congressional leaders through the weekend.
Any deal on taxes in the Senate might meet resistance in the House from conservative Republicans.
On NBC, Obama warned of the fallout in financial markets if the two sides did not reach an agreement.
"If people start seeing that on January 1st this problem still hasn't been solved, that we haven't seen the kind of deficit reduction that we could have, had the Republicans been willing to take the deal that I gave them ... then obviously that's going to have an adverse reaction in the markets," Obama said, adding that he had offered Republicans significant compromises that had been rejected repeatedly.
He said he would avoid tax increases for most Americans, even if the talks fall apart.
"If Republicans do in fact decide to block it, so that taxes on middle class families do in fact go up on January 1st, then we'll come back with a new Congress on January 4th and the first bill that will be introduced on the floor will be to cut taxes on middle class families," Obama said.
John Boehner, the speaker of the House of Representatives, rejected Obama's accusations that Republicans were not being amenable to compromise.
"The president's comments today are ironic, as a recurring theme of our negotiations was his unwillingness to agree to anything that would require him to stand up to his own party," Boehner, who has had trouble convincing his Republican colleagues to support his own proposals, said in a statement.