President Obama on Tuesday forcefully defended the deal his administration has struck with Republicans to temporarily extend Bush-era tax cuts for all income levels, saying the concessions - some of which have infuriated liberals - are necessary to avoid a tax increase for nearly all Americans at year's end.

Speaking at a news conference at the White House Obama said he would have preferred to let the tax cuts on high incomes expire, and he pledged to continue to argue that Republicans are wrong in insisting that all the cuts be extended.

But the president said allowing the stalemate to continue and the tax cuts to lapse - as some Democrats have urged - might help his party politically but "would be a bad deal for the economy and a bad deal for the American people."

"This isn't an abstract debate, this is real money for real people," he said.

Obama also spoke directly to concerns that he had ceded too much ground, comparing the tax debate to disappointment among liberals over the failure to include a so-called public option in the health-care overhaul

"This country was founded on compromise," he said.

The surprise news conference came as liberals complained loudly about the agreement announced Monday night.

Sen. Bernard Sanders (I-Vt.) called the agreement "an absolute disaster and an insult to the vast majority of the American people," and he said he would try to block it in the Senate. MSNBC host Ed Schultz called it "against the will of the American people."

Adam Green, leader of a liberal activist group called the Progressive Campaign Change Committee, said, "President Obama let down millions of voters." And Rep. John Conyers Jr., a senior House Democrat from Michigan, said he would "do everything in my power to make certain that legislation along these lines does not pass during the lame-duck session."

"I have some serious reservations about parts of this deal," Rep. Chris Van Hollen (D-Md.) said in an interview on Tuesday with Bloomberg Television. Van Hollen was the lead negotiator for House Democrats in bipartisan talks on the tax cut extension. "I understand the importance of getting to an understanding, but there are certain elements that I think will cause a great concern to members of our caucus."

Administration officials are aware of the frustration. In announcing the deal Monday night, Obama said, "I know there's some people in my own party and in the other party who would rather prolong this battle, even if we can't reach a compromise."

But it's not clear that the liberals can do anything to stop the agreement, which would extend expiring income tax cuts for all Americans, renew jobless benefits for the long-term unemployed and grant a one-year reduction in Social Security taxes paid by employees. With most Republicans and some Democrats in both houses of Congress likely to embrace the deal, it's not clear that Sanders can do much to block it.

Liberals have repeatedly backed down in similar instances in the past two years. For example, many liberal Democratic lawmakers threatened to withhold their votes from the health-care legislation Obama sought unless it included a government insurance option. But administration pressure eventually led nearly of all of them to vote for the measure.

One key difference Obama faces this time in convincing the left will be the absence of strong support from congressional leaders.

House Speaker Nancy Pelosi said nothing publicly Monday after the deal was announced, while a spokesman for Senate Majority Leader Harry M. Reid (D-Nev.) was noncommittal.

"Now that the president has outlined his proposal, Senator Reid plans on discussing it with his caucus tomorrow," Reid spokesman Jim Manley said in a statement.

Vice President Biden plans to go to Capitol Hill on Tuesday afternoon to lobby Senate Democrats - including Reid and Sanders - on supporting the agreement.