WASHINGTON -- Thousands of liberal public-option backers and conservative tea partiers launched last-chance campaigns Tuesday in the nation's capital to persuade Congress to pass -- or reject -- sweeping health care legislation.

Democratic congressional leaders conceded that they may not have the votes for final passage of the overhaul by March 26, when Congress is to break for spring recess. They're trying to persuade party moderates and abortion foes to go along. President Barack Obama wants final votes even earlier, before his March 18 departure on an overseas trip. That appears unlikely.

Republicans launched an all-out effort to derail the bill, urging congressional candidates to hold town hall meetings, organize voters over the Internet and denounce any special deals that may be cut to grease Democrats' votes. "A vote for this bill opens an entirely new line of attack on House Democrats," Johnny DeStefano, deputy director of the National Republican Congressional Committee, wrote in a memo to candidates.

The U.S. Chamber of Commerce said it will spend as much as $10 million on a television ad claiming that Mr. Obama's plan will only worsen the bad economy and job market. And Obama senior adviser David Axelrod, on a conference call Tuesday, told advocates of the legislation, "What happens in the next 10 days will be critical."

Despite their divergent goals, what these camps share is an acute understanding of what happened last year, after Democrats failed to pass the health care overhaul before the month-long congressional August recess. In the boisterous town hall meetings and small-government tea party protests that followed, all sides learned that delaying a big vote until after a recess buys the opposition time, and that public demonstrations can have an impact on the political process.

"Our intent and our hope is to have no vote take place before recess," said Mark Skoda, founder of the Memphis Tea Party and a spokesman for the "Take the Town Halls to Washington" campaign that began Tuesday.

The group's Web site asked volunteers to travel to Washington before the two-week spring recess to lean on 66 House Democratic lawmakers whom they consider to be wavering on Mr. Obama's plan: "We want to let them know there is only one vote their constituents will support: No on Obamacare."

Organizers plan to videotape the meetings and release them to constituents. The first meeting was to be Wednesday with Rep. Jason Altmire, D-Pa.

In the pro-legislation camp, thousands of supporters of Mr. Obama's plan -- many organized by unions and some dressed in hospital gowns with tubes taped to their faces -- protested outside a Washington hotel where a meeting was being held by America's Health Insurance Plans, the trade group of health insurers. Ten protesters crossed a police line, saying they were there to make citizens' arrests of insurance officials. Police hauled the 10 away.

The legislation that Mr. Obama is asking Congress to pass aims to cover 31 million more Americans and impose tighter restrictions on insurers. But some business leaders fear that it will allow health care costs to keep climbing and force them to pay for it. Many liberals don't think the legislation goes far enough but have concluded that they would rather get something than nothing.

Under one leading scenario, the House would vote on legislation that the Senate passed Dec. 24. The House would then take up a separate measure that would make changes to it. If approved, the Senate also would have to pass that measure. Since it would be brought up under "reconciliation" rules designed to speed fiscal legislation, only 51 votes would be needed for passage, and only 20 hours of debate would be permitted. Filibusters, which can be shut off only with 60 votes, aren't permitted against reconciliation bills. Democrats control 59 Senate votes.

House Democrats need 216 votes to pass the Senate bill. They control 254 of 435 House seats, with four vacancies.

Washington correspondent Daniel Malloy writes the "Pittsburgh On The Potomac" blog exclusively at PG+, a members-only web site of the Pittsburgh Post-Gazette. Our introduction to PG+ gives you all the details.