WASHINGTON -- President Barack Obama yesterday extended both a sharp stick and an olive branch to critics of his far-reaching plan to overhaul the nation's health care system, openly ridiculing those who attacked his proposal for an optional government insurance plan but also leaving the door open to compromise.

The two-pronged strategy reflected the unique challenge that Mr. Obama faces at this stage of the game, as Congress begins the long, murky process of tackling one of the most complex and politically sensitive issues on the national agenda:

On the one hand, the president is working to keep foes from seizing control of the debate and throttling his initiative before it is fully formed. On the other hand, he's trying to keep adversaries at the negotiating table in hopes of reaching a broad accord.

In his news conference yesterday, Mr. Obama threw the political equivalent of a brush-back pitch, all but jeering at critics who say his plan for a government insurance option would kill off the private companies that now supply coverage for a majority of consumers.

"If private insurers say that the marketplace provides the best-quality health care, if they tell us that they're offering a good deal, then why is it that the government, which they say can't run anything, suddenly is going to drive them out of business?" the president asked. "That's not logical."

So long as a public plan is not subsidized by tax dollars, he said, private insurers should be able to compete by making their programs more efficient and consumer-friendly.

And, in an effort to underline what's at stake for ordinary Americans in the often-arcane and confusing battle over health care policy, Mr. Obama framed his proposal as the only way to break the cycle of ever-higher medical costs that is sapping the financial stability of families and the government.

But he coupled his aggressive counterattack with a signal that he may be open to compromise. Twice side-stepping questions about his intentions, the president refused to rule out the possibility that he might sign a health care bill that did not include a public plan option. "We are still early in this process," he told reporters at White House midday news conference. "We have not drawn lines in the sand."

Mr. Obama's approach, reassuring his partisans while still hinting at compromise, comes as he intensifies efforts to shape the escalating national health care debate. The president, who last week both challenged and sought to appease doctors in a speech to the American Medical Association, will host a health care town hall meeting at the White House this evening, the second such event in the last two weeks.

He is also increasingly looking to mobilize his campaign army. With organizational support from the Democratic National Committee, the president's supporters are holding events around the country Saturday aimed at building a political consensus behind a health care bill. The events will include blood drives, medical exams and sessions on nutrition.

Drawing lessons from the defeat of former President Bill Clinton's health care push in the early '90s, when many believe that opponents did a better job of mobilizing grass-roots activism, DNC political operatives are trying to personalize the health care issue by highlighting stories of ordinary Americans frustrated with the health care system.

Fifteen years ago, the insurance industry was able to play on public fears about change with its ubiquitous "Harry and Louise" TV ads, featuring a couple fretting about the government making their health care choices. Now, Mr. Obama's campaign Web site urges people to share stories about their battles with the health care system. Supporters are also being encouraged to send letters to members of Congress.

"What opponents of health care did very well was personalize a complex issue with Harry and Louise. We think there are powerful stories to be told that argue for health care reform," said DNC national press spokesman Hari Sevugan. "Once you hear those stories, it demands reform this year."

The Obama initiative comes amid more signs of delays on Capitol Hill, where lawmakers continue to wrangle over the shape of gargantuan health care legislation being written by senior Democrats. That is feeding concerns in some quarters that the health care drive may bog down. It has also highlighted potential divisions within Democratic ranks.

Democratic proposals recently have drawn fire not just from Republicans and industry critics, but also from some moderate Democrats concerned about the reforms' cost and potential to disrupt the current health system.

Yesterday, several leaders, including Illinois Sen. Dick Durbin, the No. 2 Democrat in the Senate, acknowledged that preliminary work on the legislation likely won't be completed before Congress leaves town this week for its 10-day July 4 recess.

Lawmakers, who had hoped to send Obama health care legislation by October, are still working to figure out ways to pay for legislation expected to cost at least $1 trillion over the next decade. There is also heated debate about whether to charge employers who do not to provide health insurance to their employees and about how to structure a new government health insurance program.