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WASHINGTON - President Obama ended Thursday's White House summit by threatening to push for passage of health care reform without Republican support, and despite the daylong meeting with Democratic and Republican lawmakers, a a bipartisan agreement remained out of reach as lawmakers vowed to stick to their guns.

At the conclusion of the televised showdown, which was aimed at finding common ground between the two political parties, Obama said Republicans had only a matter of time to decide if they would jump onboard.

"If we're unable to resolve differences over health care, we will need to move ahead on decisions," he said, alluding to using reconciliation, a controversial maneuver that prevents a GOP filibuster by requiring only 51 votes to pass legislation.

Obama added that if voters are unhappy with results, then "that's what elections are for."

But Republican leaders expressed doubt after the meeting that a bipartisan agreement could be reached.

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"It's not going to be possible with that kind of an approach to come together within the timeframe that he indicated if he insists...on starting with this 2,700-page bill, then tweaking it to adopt some of our ideas," said Sen. Jon Kyl of Arizona, the No 2. Republican in the Senate.

"I don't think there will be Republican support," Senate Minority Leader Mitch McConnell, R-Ky., flatly declared.

Democratic leaders, meanwhile, seemed eager to take the president up on his threat and abandon the prospect of a bipartisan bill.

"The president said we have to do something very soon and I agree with him," Senate Majority Leader Harry Reid said. "We're willing to work with him but time is of the essence. The American people waited five decades for this. It's time we do something and we're going to do it."

The summit, in which three dozen lawmakers participated, made clear that both sides agreed that the health care system needed to be fixed, but they sharply diverged on how to do it.

Republicans remained adamant that their incremental approach reflected the will of the people and wouldn't break the bank while Democrats insisted that sweeping health care reform was the only way to fix the system.

Yet Obama held out hope that the two parties could find common ground.

"I thought it was worthwhile for us to make the effort," he said in his closing remarks. But he rejected the Republican argument to use a step-by-step approach.

"It turns out that baby steps don't get you where you need to go," he said. "If we saw significant movement, not just gestures, then you wouldn't need to start over because everyone here knows what the issues," he said. "We cannot have another yearlong debate on this."

Republicans opened the summit by urging Obama to "start over" on health care reform and to renounce an unusual move to sidestep a GOP filibuster.

Democrats responded by repeatedly highlighting several points of agreement on health care reform with the GOP in an effort to show that it made no sense to start over again.  They also cast the reform they want as critical to tackling an issue that is even more pressing to many Americans -- the struggling economy.

Yet Democrats were unable to overcome the points of disagreement that prevented a bipartisan breakthrough.

Early on in the summit, the president clashed with Republicans over whether his health care proposal, which is modeled after the Senate version that passed on Christmas Eve, would lower premium rates.

Sen. Lamar Alexander, R-Tenn., said the Congressional Budget Office, which is the official scorekeeper on Capitol Hill legislation, noted that premiums will rise in the individual market under the Senate bill.

Obama shot back that Alexander's claim was "not factually accurate," arguing that premiums would go down 14 to 20 percent for families who keep their same coverage.

"What the Congressional Budget Office says is that because now they've got a better deal, because policies are cheaper, they may choose to buy better coverage than they do right now," Obama said. "That might be 10 to 13 percent more expensive than the bad insurance they had previously."

The heated exchange set the tone for a meeting that Democrats dominated by speaking for most of the morning session, according to Senate Minority Leader Mitch McConnell, who at one point noted that Democrats had spoken for 56 minutes compared to 24 minutes for Republicans.

But Republicans used their limited time to repeatedly slam the Democratic health care bill, with a harsh critique coming from Sen. John McCain, Obama's opponent in the 2008 presidential race.

McCain blasted the steps Democrats have taken over the past year to advance the legislation, including striking backroom deals with the drug manufacturing lobby, and other arrangements that favored certain states with reluctant Democratic senators.

"I hope that would be an argument for us to go through this 2,400-page document, remove all the special deals for the special interests that favor the few and treat all Americans the same ... so that they will know that geography does not dictate what kind of health care they would receive," McCain said.

Obama told McCain that they're no longer campaigning.

"The election is over," Obama said.

"I'm reminded of that every day," McCain said with a laugh.

Throwing diplomacy to the wind, House Minority Leader John Boehner came out swinging during the second half of the summit, telling Obama that he believes the Democratic version of health care reform would "bankrupt our country" and is a "dangerous experiment."

"We may have problems in our health care system but we do have the best health care system in the world by far and having the government take over health care... is a dangerous experiment with the best health care system in the world that I don't think we should do."

Boehner echoed his GOP colleagues in urging Obama to scrap the bill and start over. The Ohio Republican criticized elements of the bill when it was his turn at the microphone during Obama's health summit Thursday.

Boehner rejected proposed tax increases and said $500 billion in projected Medicare savings should be used to keep the program solvent. He said requiring people to buy health insurance is unwise and possibly unconstitutional, and fining employers that don't provide their workers with health coverage would drive up unemployment.

Obama dismissed Boehner's criticism as "the standard talking points that Democrats and Republicans have had for the last year."

"And that doesn't drive us to an agreement on issues," the president said, adding that Boehner's argument "based on my analysis, just isn't true."

Up until those sharp exchanges, both political sides had maintained a mostly diplomatic tone. But the high-stakes summit exposed deep political fault lines neither side was sure could be straddled.

"We have a very difficult gap to bridge here," Virginia Rep. Eric Cantor, the No. 2 Republican in the House, said in reference to Democrats' stalemated legislation to extend coverage to more than 30 million people who are now uninsured. "We just can't afford this. That's the ultimate problem."

Obama said both parties should focus on areas they agree on, like reducing health care costs, and areas where they disagree -- "and at the end of that process then make an honest assessment about whether we can bridge these differences."

"I don't know yet whether we can," the president said. "My hope is that we can. I'm going to be very eager to hear and explore how we might do so."

The summit began with Republicans urging Democrats to hit the reset button on health care reform.

Democratic leaders argued back, saying it was too late to start over and claiming that most Americans want health care reform now.

A new poll, however, shows that Americans are more concerned about the nearly 10 percent unemployment rate than they are about health care reform.

Forty-six percent of Americans say creating jobs should be the government's top priority, according to a Zogby International-University of Texas Science Center poll. Only 18 percent said health care reform was the top issue on their list.

But Thursday's summit at Blair House was called for a bipartisan discussion of health care, and Republicans took the opportunity to tell the president to his face that he should start from scratch and go "step by step" in reducing health care costs.

"We believe we have a better idea," Sen. Lamar Alexander, R-Tenn, told the president in his opening remarks for Republicans, arguing that his party represents the views of a great number of Americans who oppose the Democratic approach.

"This is a car that can't be recalled and fixed, and we ought to start over,"Alexander said.

Senate Majority Leader Harry Reid rejected Alexander's call for a promise from Democrats that they wouldn't use reconciliation -- a controversial procedural move that would pass a bill with a simple majority of 51 votes -- to push their health care plan through alone.

Reid said that reconciliation -- often called the "nuclear option" -- isn't the only way to pass the health care overhaul. But he added that Republicans can't pretend it's never been used before to push a bill through. Reid said Republicans are entitled to their own opinions, but not their own facts, in the health care debate.

Leaving the site during a lunch break, Obama was asked by waiting reporters if he thought the debate was engendering a lot of interest across the country.

"I don't know if it's interesting watching it on TV," he responded. But Obama also said, "I think we're establishing that there are actually some areas of real agreement. And we're starting to focus on what the disagreements are."

"If you look at the issue of how much government should be involved," he said, "the argument that the Republicans are making really isn't that this is a government takeover of health care but rather that we're ensuring the ... We're regulating the insurance market too much. And that's a legitimate philosophical disagreement."

Polls show Americans want their elected leaders to address the problems of high medical costs, eroding access to coverage and uneven quality. But the public is split over the Democrats' sweeping legislation, with its $1 trillion, 10-year price tag and many complex provisions, including some that wouldn't take effect for another eight years -- after Obama has packed up and left the White House.

Fox News' Dominique Pastre, and The Associated Press contributed to this report.