President Barack Obama said on Thursday the United States faces a national crisis and pressed Congress to urgently pass a jobs package of tax cuts and government spending he is proposing to revive the stalled economy.

The cost of Obama's plan would be $447 billion, a Senate Democratic aide told Reuters.

With his poll numbers at new lows amid voter frustration with 9.1 percent unemployment, Obama was poised to use a high-stakes address to Congress to pitch a sweeping economic plan that is critical to his re-election chances but he faces an uphill fight with Republicans.

It will provide a jolt to an economy that has stalled and give companies confidence that if they invest and hire there will be customers for their products and services. You should pass this jobs plan right away, Obama said in excerpts of a televised speech he will deliver at 7 p.m. EDT (2300 GMT).

Taking aim at Republicans who have consistently opposed his initiatives, Obama said it was time to stop the political circus and actually do something to help the economy.

Obama, who pushed through an $800 billion economic stimulus package in 2009, said his jobs plan would cut taxes for workers and businesses and put more construction workers and teachers on the job through infrastructure projects.

It will provide a tax break for companies who hire new workers and it will cut payroll taxes in half for every working American and every small business, he said.

Obama is seeking to seize the initiative in his bitter ideological battle with Republicans, ease mounting doubts about his economic leadership and turn around his presidency just 14 months before voters decide whether to give him a second term.

Obama wants Congress to pass his American Jobs Act by the end of this year. But that may be hard to achieve with politicians already focusing on the presidential and congressional elections in November 2012.

If Obama can push through his plan, it might provide an economic boost quickly enough for him to reap political benefits. If it stalls in a divided Congress, his strategy will be to blame Republicans for obstructing the economic recovery.

Obama is making payroll tax relief for workers and their employers the centerpiece of his package. He is also proposing further jobless benefits and new investment to rebuild roads, bridges and other crumbling infrastructure plus help states to prevent further layoffs.

How much of the jobs package is viable remains in question. Almost all of it ultimately depends on winning support from Republicans who control the House of Representatives and have consistently opposed Obama's spending initiatives.

Bipartisan cooperation could be hard to come by in Washington's climate of political dysfunction where a bruising debt feud this summer brought the country to the brink of default and led to an unprecedented U.S. credit downgrade.

But Obama will insist that everything in here is the kind of proposal that's been supported by both Democrats and Republicans -- including many who sit here tonight, and everything in this bill will be paid for. Everything.

(Additional reporting by Laura MacInnis, Jeff Mason, Doina Chiacu, Tim Reid, Tom Ferraro, Alister Bull and David Lawder; writing by Matt Spetalnick, Editing by John O'Callaghan)