In a letter to congressional leaders, Obama defended last year's huge economic stimulus package, saying it helped break the economy's free fall, but argued that more spending is urgent and unavoidable. "We must take these emergency measures," he wrote in an appeal aimed primarily at members of his own party.

The letter comes as rising concern about the national debt is undermining congressional support for additional spending to bolster the economy. Many economists say more spending could help bring down persistently high unemployment, but with Republicans making an issue of the record deficits run up during the recession, many Democratic lawmakers are eager to turn off the stimulus tap.

"I think there is spending fatigue," House Majority Leader Steny H. Hoyer (D-Md.) said recently. "It's tough in both houses to get votes."

Democrats, particularly in the House, have voted for politically costly initiatives at Obama's insistence, most notably health-care and climate change legislation. But faced with an electorate widely viewed as angry and hostile to incumbents, many are increasingly reluctant to take politically unpopular positions.

The House last month stripped Obama's request for $24 billion in state aid from a bill that would extend emergency benefits for jobless workers. Senate Majority Leader Harry M. Reid (D-Nev.) hopes to restore that funding but with debate in that chamber set to resume this week, he acknowledges that he has yet to assemble the votes for final passage. Obama's request for $23 billion to avert the layoffs of as many as 300,000 public school teachers has not won support in either chamber.