U.S. President Barack Obama Saturday urged lawmakers to find a way to raise the country's borrowing capacity by Tuesday and stave off a looming debt default crisis, amid this weekend's frantic beat-the-clock efforts to strike a deal.

"We need to reach a compromise by Tuesday so that our country will have the ability to pay its bills on time -- bills like social security checks, veterans' benefits, and contracts we've signed with thousands of American businesses," Obama said in his weekly radio and Internet address.

The U.S. federal government's borrowing limit, currently at 14.29 trillion U.S. dollars, was reached on May 16. The Treasury Department said the nation would begin to default on its debts unless Congress agreed to lift the limit by Aug. 2.

"If we don't, for the first time ever, we could lose our country's Triple A credit rating. Not because we didn't have the capacity to pay our bills--we do-- but because we didn't have a Triple A political system to match it," Obama said, reiterating his stance made at a White House press conference on Friday.

Obama urged U.S. lawmakers to ditch entrenched partisanship and find a bipartisan compromise plan as soon as possible.

However, the Democratic-controlled Senate on Friday night rejected a modified two-stage plan put forth by House Speaker and No. 1 Republican John Boehner that was passed by the lower chamber. In an unusual Saturday session, the Republican-controlled House also rejected an alternative solution put forward by Senate Majority (Democratic) Leader Harry Reid and favored by the White House.

The fact that Republicans and Democrats remain at loggerheads on a tangible compromise plan adds fresh uncertainty to the debt gridlock.

Saturday's House vote was 173 to 246 on the measure aimed at lifting the debt limit by 2.4 trillion dollars and cutting spending by 2.2 trillion dollars over a decade.

Experts said the vote was largely symbolic, but could pay the way for further concessions in negotiations.

In a similar move, 43 Republican senators Saturday voiced opposition to the Reid debt ceiling plan, saying it failed to alter the spending trajectory that is putting the U.S. economy and national security at risk.

"We will not vote for your 2.4 trillion U.S. dollars debt limit amendment which, if enacted, would result in the single largest debt ceiling increase in the history of the United States," noted a letter signed by these senators including Senate Republican leader Mitch McConnell.

Top GOP and Democratic congressional leaders continued with their fingers pointing at each other after the House vote.

The nation is at "a crucial time" in history, and the stakes of failing to find a compromise are quite high, Reid told reporters Saturday.

The U.S. has no more time for delaying tactics, Reid said before heading for the White House to update the president on the status quo of the debt ceiling negotiations.

"We know that the Reid bill will not pass the Senate," McConnell told a press conference Saturday shortly after the House vote, adding that it was time to end the "charade" and get serious on finding a compromise plan.

House Speaker Boehner challenged him at the press conference, saying it was the time for the president to tell Americans what plan he was for.

But Boehner and McConnell also said they were confident the deadlock would be resolved soon.

McConnell said he was "fully engaged" with the White House to find a possible deal.

Despite the optimism voiced by GOP leaders, Reid struck a cautious note on the Senate floor after returning from the White House meeting, saying the engagement was not in a meaningful way, as Republican leaders refused to negotiate in good faith.

A procedural Senate vote on Reid's proposal had been scheduled for 0500 GTM Sunday, but was postponed until 1700 GMT to give negotiators more time to work out an agreement.

But analysts said the upcoming Senate test vote was largely symbolic unless there will be a compromise achieved, as the 43 Republican senators signing the joint letter were enough to block the measure.

Moreover, the House's rejection came even before the Senate voted on the Reid plan. "There is very little time," Obama noted in his weekly address, adding that there are plenty of bipartisan compromise ways to lift the nation out of this mess.