US President Barack Obama is pictured during a news conference in the Brady Press Briefing Room of the White House in Washington, July 15, 2011. [Photo/Agencies]

WASHINGTON - US President Barack Obama appealed for public support Saturday to push Congress to avert an unprecedented default on America's national debt as lawmakers worked on dual tracks to reach an elusive deal.

Obama wants US lawmakers to approve a giant package that would not only prevent a default by raising the government's borrowing limit, but also slash trillions of dollars from the country's enormous deficit. He challenged lawmakers "to do something big."

But opposition Republicans, who control the House of Representatives, reject Obama's proposal to raise some taxes in addition to cutting spending. They plan to vote next week on legislation that would tie an increase in the debt limit to a constitutional amendment requiring a balanced budget. Such an amendment is unlikely to get enacted.

In the Senate, the Republican and Democratic leaders worked on a bipartisan plan that would allow Obama to raise the debt limit without a prior vote by lawmakers. The talks focused on how to address long-term deficit reduction in the proposal in hopes of satisfying House Republicans.

As a critical August 2 deadline approached, the chances that Obama would get $4 trillion or even $2 trillion in deficit reduction on terms he preferred were quickly fading as Congress moved to take control of the debate. At a news conference Friday, Obama opened the door to a smaller package of deficit reductions without revenue increases.

Obama's communications director, Dan Pfeiffer, said the president, vice-president Joe Biden and White House aides were discussing "various options" on Saturday with congressional leaders and House and Senate aides from both parties.

The White House held out the possibility of arranging a meeting with the leaders on Sunday.

In his weekly radio and Internet address, Obama appealed to the to the public in hopes of influencing a deal that talks have failed to produce so far.

"We have to ask everyone to play their part because we are all part of the same country," Obama said Saturday, pushing a combination of spending cuts and tax increases that has met stiff resistance from Republicans. "We are all in this together."

Obama said the wealthiest must "pay their fair share." He invoked budget deals negotiated by Republican President Ronald Reagan and Democratic House Speaker Tip O'Neill, and Democratic President Bill Clinton and Republican Speaker Newt Gingrich.

"You sent us to Washington to do the tough things, the right things," he said. "Not just for some of us, but for all of us."

A weekend deadline that the president gave congressional leaders to choose one of three deficit reduction options became a moot point after House and Senate leaders made it clear to the White House on Friday that they were moving ahead with their own plans.

In the Republicans' weekly address Saturday, Sen. Orrin Hatch of Utah argued for passage of a balanced-budget amendment. He blamed Democrats for failing to embrace adequate budget cuts and said "the solution to a spending crisis is not tax increases."

An amendment that requires a balanced budget, he said, "would put us on a path to fiscal health and would prevent this White House or any future White House from forcing more debt on the American people."

The government said Friday it was using its last stopgap measure to avoid exceeding the current $14.3 trillion debt limit. Administration officials, economists and the financial markets have warned that missing the August 2 deadline and precipitating a government default would send convulsions through an already weakened economy.

Obama had held five straight days of meeting with congressional leaders at the White House, but none of the three options he proposed - deficit cuts of $4 trillion, $2 trillion or $1.5 trillion over 10 years - were unlocking enough support to increase the debt ceiling by the $2.4 trillion Obama wants to make it last beyond the 2012 elections.

Essentially declaring those discussions over, Senate Republican leader Mitch McConnell said Friday: "Now the debate will move from a room in the White House to the House and Senate floors."

In search of a deal, Obama has used a combination of private meetings with congressional leaders and high visibility press conferences, radio addresses and public statements in an effort to win the public to his side. His pitch is also aimed at independent voters, to whom he is presenting himself as a willing compromiser.