WASHINGTON - After weeks of intense partisanship, Republican congressional leaders and U.S. President Barack Obama made a last-minute stab at compromise Saturday to avoid a government default threatened for early next week.

But there was no undisputed evidence of progress by day's end, only expressions of anxiety among lawmakers that a potentially crippling blow to the nation's economy was drawing uncomfortably close. The deadline for raising the nation's debt limit and averting an unprecedented U.S. default was just three days away.

"We are now fully engaged, the speaker and I, with the one person in America out of 307 million people who can sign a bill into law," Senate Republican leader Mitch McConnell said at a joint news conference with House Speaker John Boehner.

"I'm confident and optimistic that we're going to get an agreement in the very near future and resolve this crisis in the best interests of the American people."

But McConnell's upbeat assessment triggered an unusually pointed rebuttal from Senate Majority Leader Harry Reid.

"That's not true," said the Nevada Democrat after returning from a meeting at the White House with Obama and House Democratic leader Nancy Pelosi.

Adding further confusion, the White House declined comment on the day's developments.

That left prospects for a compromise murky.

The renewed negotiations occurred on one track, while another pointed the Senate toward a 1 a.m. test vote on legislation to raise the debt limit while cutting spending by $2.4 trillion.

That measure was introduced by Reid but opposed by Republicans, who vowed to prevent it from advancing.

Halfway around the world, on a visit to Camp Leatherneck in Afghanistan, the nation's top military officer fielded questions from troops asking if they would be paid in the event of a default.

"I actually don't know the answer to that question," said Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, although he told them they would continue to go to work each day.

Without legislation in place by next Tuesday, administration officials say the Treasury will run out of funds to pay all the nation's bills. They say a subsequent default could prove catastrophic for the U.S. economy and send shockwaves around the world.

The president is seeking legislation to raise the government's $14.3 trillion debt limit by about $2.4 trillion, enough to tide the Treasury over until after the 2012 elections. Over many weeks, he has agreed to Republican demands that deficits be cut -- without a requirement for tax increases -- in exchange for additional U.S. borrowing authority.

But Obama has threatened to veto any legislation that would require a second vote in Congress for any additional borrowing authority to take effect, saying that would invite a recurrence of the current crisis in the heat of next year's election campaigns.

Saturday's developments opened with Obama saying, "There is very little time" in his weekly radio and Internet address.

A few hours later, House Republican leaders engineered a vote to defeat a Reid-drafted proposal to raise the debt limit on a near-party line vote at mid-afternoon.

Arguing into the night, Republicans stood ready to block the same measure's advance in the Senate.

Reid accused Republicans of filibustering, and it appeared he was hoping to find enough defectors in the GOP ranks so he could overcome the blockade.

In contrast to McConnell, Reid said individual Republicans had shown a willingness to compromise.

Indeed, some Republicans expressed concerns about the effects of gridlock.

"I'm worried about Congress defaulting on our country," said Sen. Johnny Isakson, R-Ga., urging lawmakers to find common ground. He suggested that spending cuts take place automatically if necessary to ensure the debt limit does not expire before 2013.

With financial markets closed for the weekend, lawmakers had a little breathing room, but not much. Asian markets begin opening for the new work week when it is late Sunday afternoon in the capital.

In his remarks at a news conference, McConnell said Obama "needs to indicate what he will sign, and we are in those discussions."

He said later he had spoken several times during the day with Vice President Joe Biden, who played a prominent role in earlier attempts to break the gridlock that has pushed the country to the verge of an unprecedented default.

Boehner said that despite the partisanship of recent weeks, "I think we're dealing with reasonable, responsible people who want this crisis to end as quickly as possible and I'm confident it will."

To get to the endgame, Republicans and Democrats had to go through the formality of killing each other's bills --- scoring their own political points -- before they could turn to meaningful negotiations.

Still, the sudden talk of compromise contrasted sharply with the day's earlier developments as both the House and Senate convened for unusual Saturday sessions.

The House voted down legislation drafted by Democrat Reid to raise the government's debt limit by $2.4 trillion and cut spending by the same amount.

The vote was 246-173, mostly along party lines and after debate filled with harsh, partisan remarks.

Republicans said the Reid spending-cuts plan was filled with gimmicks and would make unacceptable reductions in Pentagon accounts. "It offers no real solutions to the out-of-control spending problems," said Rep. Alan Nunnelee of Mississippi, part of a group of 87 first-term Republicans who have led the push for deeper spending cuts.

Not even Democrats seemed to like the legislation very much, although many emerged from a closed-door meeting of the rank and file saying they would vote for it.

Rep. Lloyd Doggett, D-Texas, called it "the least worst alternative to avoid default."

Yet with their votes, many Democrats signaled their readiness for compromise by voting to cut spending without raising taxes. Many Republicans insist taxes must not be raised to cut into federal deficits, even for the wealthiest Americans and for big oil companies.

In remarks on the House floor, Rep. David Dreier, R-Calif., said the vote itself could be prelude to a final effort at compromise that would involve the White House and the leaders of both parties.

Across the Capitol, the Senate marked the hours before a scheduled test vote at 1 a.m. Sunday on the same measure.

There was no doubt about the outcome there, either, unless compromise intervened.

A total of 43 Republicans sent Reid a letter saying they would block the bill from advancing, enough to prevail.

With both parties' preferred solutions blocked, the only alternatives were compromise that was so far elusive or a default that no one claimed to want.

The day's events in the House were orchestrated as political payback, and unusual at that, since Republicans lined up to kill legislation that hadn't even cleared the Senate.

Less than 24 hours earlier, Reid had engineered the demise of a House-passed bill hours after it passed, and without so much as a debate on its merit.

Pelosi said Boehner "chose to go to the dark side" when he changed his own legislation to satisfy tea party lawmakers and other critics.

There were catcalls from the Republican side of the aisle at that, and Pelosi responded by repeating that the speaker "chose to go to the dark side."

Republicans ridiculed Reid's legislation.

"Not only does it fail to address our spending and debt problem, it won't even prevent a downgrade of our credit rating," said Rep. Scott Garrett, R-N.J. "We need actual cuts to government spending to address our long-term debt crisis, not phantom cuts and accounting gimmicks."