President Obama attempted to reinvigorate support for his struggling health care agenda on Monday by giving a stirring campaign-style speech in Cincinnati to thousands of union members celebrating Labor Day.

After a turbulent summer, during which opponents seized control of the health care debate and liberals criticized the president as not pushing forcefully enough for reform, Obama stepped back into the fray, shirtsleeves rolled up, with an emphatic defense of his policies and his young presidency.

"I've got a question for all these folks who say, 'You know, we're going to pull the plug on Grandma' and 'This is all about illegal immigrants' - you've heard all the lies," Obama said, diverging from his prepared remarks. "I've got a question for all those folks: What are you going to do? What's your answer? What's your solution?

"And you know what? They don't have one," he said.

In abandoning the cool, patient tone he adopted at health-care town hall meetings over the summer, Obama signaled that he is ready to take a hard-line approach tomorrow, when he will deliver a crucial address on reform to a joint session of Congress. He has declined to take firm positions on specific elements of a bill, preferring to leave details to lawmakers, who are returning from their summer recess today with a pile of issues still to be addressed. House Democrats are struggling to find consensus in their caucus. In the Senate, Finance Committee Chairman Max Baucus, a Montana Democrat, circulated his own plan over the weekend among the bipartisan "Gang of Six" on his panel, sidestepping a government-run, or public, insurance option. He proposed taxing insurance companies that offer the most comprehensive coverage as a way to limit the cost of reform.

The president told the supportive crowd at an amusement park for the annual AFL-CIO Labor Day gathering that the debate period is over.

"There comes a time to decide, a time to act. And Ohio, that time is now," he said, a direct retort to Republicans who have suggested he go back to the drawing board on reform.

Obama drew wild applause when he reiterated his support for a government-run insurance plan, a key change that labor officials strongly support.