WASHINGTON — Six months in office, President Barack Obama sought Wednesday night to rally support for sweeping health care legislation as Congress struggled to find agreement on a historic overhaul. He vowed to reject any measure "primarily funded through taxing middle-class families."

During a prime-time news conference, Obama defended his decision to set a midsummer deadline for the House and Senate to act, even if it isn't met. "I'm rushed because I get letters every day from families that are

being clobbered by health care costs, and they ask me can you help," he said.

The stakes are huge not just for everyday Americans, but also for Obama, who is putting much of his credibility on the line to gain congressional passage. His stepped-up public role comes as he faces rising criticism from Republicans, sliding public approval ratings and divisions within his party. Obama acknowledged that many people are uneasy about growing federal budget deficits and the fast-rising government debt.

He said that without a deadline for action, a recent proposal to curtail the growth in Medicare costs would not have materialized "until who knows when." He said in the past few days, leaders in both houses had agreed to incorporate it into legislation taking shape.

Obama stepped to the microphone looking grayer than the man who ran for president and took office in January.

He said that since he moved into the White House, "we have been able to pull our economy back from the brink."

Yet he said, "of course we still have a long way to go." Obama didn't say so, but unemployment is expected to remain stubbornly high for many months to come.

He moved quickly into his pitch for health care legislation, an issue that towers above all others — and has led at least one Republican to say that it could prove to be the president's Waterloo if the drive collapses.

"This isn't about me. I have great health insurance and so does every member of Congress," Obama said.

The president said that in addition to helping millions who lack coverage, the health care legislation is central to the goal of eventually rebuilding the economy stronger than it was before the recession that began more than a year ago.

He said Medicare and Medicaid, government health care programs for the elderly and the poor, are the "biggest driving force behind our federal deficit."

Unless they are tamed, he said to a national TV audience, "we will not be able to control our deficit. If we do not reform health care, your premiums and out-of-pocket costs will continue to skyrocket."

The president said he thinks it is possible to fund more than two-thirds of the cost of health care legislation by eliminating waste and redirecting federal funds already being spent. The rest must come from higher taxes, he said.

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The administration last winter proposed a plan to raise taxes on upper-income wage earners by limiting their ability to claim deductions.

Congress looked unfavorably on the proposal, and Obama said he was open to alternatives — with one notable exception.

"If I see a proposal primarily funded through taxing middle-class families, I'm going to be opposed to it," he said.

It was not immediately clear whether the president was signaling he would accept at least some higher taxes on middle-class families as the price for winning passage.

Obama's words came as House Speaker Nancy Pelosi said Democrats have the votes to pass a massive health care bill in that chamber, prompting surprise and some criticism from conservatives within her party.

Congress is struggling to figure out how to pay for adding millions to the ranks of the insured and slowing the long-term costs of health care in the United States.

In his comments, Obama reiterated his pledge that any bill he signs will not add to the nation's soaring deficit. "And I mean it," he said.