President Barack Obama makes an opening statement during a news conference in the East Room of the White House in Washington, Wednesday July 22, 2009. AP Photo/Pablo Martinez Monsivais

President Barack Obama said Wednesday night that Medicare and Medicaid are the "biggest driving force behind" massive federal deficits, and must be tamed as part of any health care legislation.

At a prime-time news conference marking six months in office, Obama said health care legislation was key to a strong economic recovery, and he added, "If we do not control these costs, we will not be able to control our deficit."

The president noted he took office with the economy in the worst recession in half a century. "As a result of the action we took in those first weeks, we have been able to pull our economy back from the brink," he said.

The president stepped to the microphone as Congress labored over his call for sweeping legislation to expand health care to millions who lack it, as well as control the costs of medical care generally.

In his opening statement, he stressed the second of those two goals.

"In the past eight year, we saw the enactment of two tax cuts, primarily for the wealthiest Americans, and a Medicare prescription program, none of which were paid for."

He vowed anew that he wouldn't sign health care legislation that wasn't paid for, although his administration has exempted from that pledge an estimated $245 billion to raise Medicare fees for doctors.

"This debate is not a game for these Americans, and they cannot afford to wait for reform any longer," Obama said. "They are looking to us for leadership. And we must not let them down."

"This debate is not a game for these Americans, and they cannot afford to wait for reform any longer."

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 passage of congressional legislation. His stepped-up public role comes as he faces rising criticism from Republicans, sliding public approval ratings and divisions within his party.

Holding his 10th extended news conference, Obama was renewing a message that the White House says he cannot pound enough: making health coverage affordable and sustainable is so vital that anything less will erode the economic stability of families, businesses and even the government.

The complex work of getting bills through the House and Senate is proving difficult. Republican leaders contend Obama's effort and the emerging bills are rushed and risky, and members of Obama's own Democratic Party are split on how to structure and pay for a daunting overhaul.

Obama sought to get beyond that and connect with Americans - and, in turn, the White House hopes, to pressure Congress. "I understand how easy it is for this town to become consumed in the game of politics, to turn every issue into a running tally of who's up or who's down," he said.

His 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 U.S.

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.

Meanwhile, a nervous public is being hit by TV ads and claims from all sides.

And other issues haven't gone away as Obama steps before the cameras. Still looming are an economy that keeps losing jobs, wars in Iraq and Afghanistan and Obama's January deadline to shut down the Guantanamo Bay detention facility.

The timing is critical as Obama appeals Wednesday night to a national viewing audience.

He wants the House and Senate to vote on comprehensive health care bills before they break for the summer, a window that is scheduled to shut by the first week in August. That timetable is growing tenuous, though, with up-and-down developments by the day.

So Obama is everywhere on health care: giving Rose Garden statements, visiting health clinics, talking to bloggers, granting interviews.

"He's prepared to do this as many times as he has to," said Michael Traugott, a University of Michigan professor who specializes in political communications. "The president has a special advantage because he's readily identifiable. The Congress is a less well known institution, and less popular in the public's eye."

Obama's approval rating stands at 55 percent, according to a new Associated Press-GfK poll, down from 64 percent in late May and early June. Some 50 percent approve of his handling of health care, but 43 percent disapprove, and that number has risen sharply since April.

With public opinion still waiting to be shaped on health care, and with the legislative details in flux, what's clear is that people care.

Nearly 80 percent of those polled say health care is an important issue to them. Obama is seeking to extend coverage to millions who don't have it and to hold down the long-term costs of health care. How to pay remain a complex political question.

It didn't help the White House when the Congressional Budget Office last week said the bills moving through Congress would add to the nation's long-term costs, not reduce them. Obama has been emphatic that he will not sign a bill that adds to the government's deficit.

Meanwhile, unemployment is at 9.5 percent and rising.

Talk of Obama inheriting an economic mess from George W. Bush is fading, and the American public is now grading the new president. His approval rating on handling the economy has been slipping as impatience grows.

Obama says the country is moving in the right direction, and he points to legislation from his first half-year in office: a massive economic stimulus bill that is ultimately designed to work over two years, a law to overhaul the credit card industry, and another to keep tobacco companies from marketing to kids.

Still, he told CBS News on Tuesday: "As long as the economy is still shedding jobs and people don't feel confident about a recovery, then, you know, I think there's going to continue to be frustration. And rightfully so."

White House spokesman Josh Earnest said Wednesday that Obama is "feeling optimistic that he's on track, after his first six months in office, to fulfill his promise to sign a health care reform bill before the end of the year."

(Copyright 2009 by The Associated Press. All Rights Reserved.)