With time running out, House Speaker John Boehner blasted the Obama administration on Thursday, saying "the White House has to get serious" in talks to avert the "fiscal cliff."
His comments sent stocks lower. (Read More: Stocks Erase Gains Amid Boehner Comments.)
Boehner spoke after meeting with Treasury Secretary Timothy Geithner, President Barack Obama's chief negotiator in the negotiations.
Facing a Dec. 31 deadline, Boehner criticized Obama for planning "campaign-style rallies," such as a scheduled apperance by the president Friday at a toy manufacturing company in Pennsylvania.
"The Democrats have yet to get serious about real spending cuts," Boehner said, adding that no subtstantive progress had been made in the past two weeks.
"Jobs are on the line, the American economy is on the line, and this is a moment for adult leadership. ... The White House has to get serious."
Earlier, some Republicans expressed pessimism about a deal to avoid the fiscal cliff, when more than half a trillion in tax increases and spending cuts would automatically go into effect.
"It is not going to happen soon," Republican Sen. John Barrasso of Wyoming, the Senate's fourth-ranking Republican, said in a Fox Business News interview Wednesday evening.
"I think right now" it's "a little bit of a standoff," Sen. John Thune, the third-ranking Republican in the Democratic-controlled Senate, told CNN late Wednesday.
Obama and Boehner conferred by phone for 15 minutes Wednesday night, their first one-on-one discussion in five days, amid increasing anxiety that the White House and top Republicans are wasting time needed to negotiate a way out of the crisis.
The schedule of Geithner's meetings suggested relatively contained chats with Republicans rather than intensive negotiations.
The Treasury secretary met first with Senate Democratic Leader Harry Reid, then headed to a session with Republican leaders of the House, including Boehner, Majority Leader Eric Cantor and House Budget Committee Chairman Paul Ryan, fresh off his Republican vice presidential campaign.
Boehner characterized the talks as "frank and direct." "I was hopeful we'd see a specific plan for cutting spending," he said, but added that he "remained hopeful" a deal can be reached.
The president's emissaries will lunch with Republican Senate Minority Leader Mitch McConnell followed by a meeting with House Minority Leader Nancy Pelosi.
There has been little evident progress in negotiations between the two sides. Republicans complain that the White House is slow-walking the talks and has yet to provide specifics on how Obama would curb the rapid growth of benefit programs like Medicare and Medicaid.
"We have not seen any good-faith effort on the part of this administration to talk about the real problem that we're trying to fix," Cantor said.
At immediate issue is whether the tax cuts that originated in the administration of President George W. Bush should be extended beyond Dec. 31 for all taxpayers including the affluent, as Republicans want, or just for less wealthy taxpayers, with income under $250,000, as Obama wants.
Obama is mounting a public campaign to build support and leverage in the negotiations, appearing at the White House with middle-class taxpayers and launching a campaign on Twitter to bolster his position.
"Right now, as we speak, Congress can pass a law that would prevent a tax hike on the first $250,000 of everybody's income," Obama said. "And that means that 98 percent of Americans and 97 percent of small businesses wouldn't see their income taxes go up by a single dime."
Obama is also hosting a private lunch on Thursday for his defeated Republican rival Mitt Romney. The president has cast his victory over Romney as a sign that Americans back his tax proposals, which were a centerpiece of his re-election campaign.
Despite a few cracks in Republican ranks, most notably from Republican Rep. Tom Cole of Oklahoma, neither side has budged significantly from its position, leaving the markets and political analysts alike to grasp at wording nuances.
It's become clear during the post-election lame-duck session of Congress that until the two sides get over the immediate tax issue, they will not move forward to serious discussions on longer-term deficit reduction and tax reform, though both have expressed interest in doing so.
Keeping the nation in suspense down to a white-knuckled deadline has become the rule rather than the exception for Congress in recent years.
Whether the risk has been a government shutdown or, as in the events that led to the fiscal cliff, default for failure to raise the U.S. government's borrowing power, Republicans and Democrats have needed the pressure of time and possible disaster to bring them together.
The last standoff, over the debt ceiling in 2011, was settled by scheduling across-the-board automatic-budget cuts of about $500 billion - the sequestration part of the fiscal cliff - to take effect just as the tax cuts expire.
While little visible progress has been made on either element of the cliff, Congress could make quick work of it once a deal is reached, as no elaborate legislation is necessarily required just to get passed the twin deadlines.
Once "off that fiscal cliff," said Thune, "and we're on to the New Year and the markets will be happy. And the people will smile."
More From CNBC
Blankfein: Seems Like 'Fiscal Cliff' Deal Could Be 'Reachable'
Obama: Let's Get 'Fiscal Cliff' Deal Before Christmas
Volcker Says Rule Is Already Changing Wall Street