WASHINGTON — Democrats maneuvered a massive overhaul of the nation's health care system toward a make-or-break vote in the House on Saturday, getting a last-minute appeal from President Barack Obama to pass his top domestic priority.

"This is our moment to deliver," Obama said.

Emerging from a closed-door meeting with the president, Speaker Nancy Pelosi predicted the bill will pass. "We can associate ourselves with the work of those who passed Social Security, those who passed Medicare," she said.

Meeting with Democrats in a rare Saturday visit to Capitol Hill, Obama said they were approaching what may be their finest moment in politics.

Later, in public remarks in the White House Rose Garden, Obama said, "What's in our grasp right now is a chance to prevent a future where every day, 14,000 Americans continue to lose their health insurance, and every year, 18,000 Americans die because they don't have it."

The bill survived a test vote with a 50-vote margin in a 242-192 roll call, but the vote on final passage was expected to be much closer. Fifteen Democrats joined all 177 Republicans in voting to block the debate.

"This bill will force my constituents to buy insurance whether it makes sense for them or not," said Rep. Cynthia Lummis, R-Wyo.

Obama made his trip to the Capitol complex as abortion rights lawmakers voiced anger at a last-minute concession granted to foes of the procedure, who were given a vote on their proposal for stronger restrictions on abortion coverage.

"There is a risk" that some in the Pro-Choice Caucus would vote against the legislation if the stricter curbs are adopted, said Rep. Diana DeGette, D-Colo.

The bill would cost $1.2 trillion over the next decade. It would provide health coverage to tens of millions of Americans who don't have it now, require most employers to offer it to their workers and prohibit insurance companies from denying coverage based on a person's medical history.

"The status quo is unaffordable and unsustainable. Health care reform benefits all of us," said Rep. Allyson Schwartz, D-Pa., as debate opened on the House floor.

House passage of the bill is crucial if Obama is to fulfill the biggest promise of his campaign last year. But the legislation still faces multiple hurdles, and a Senate vote on it might not occur until next year.

Republicans were united in their opposition.

"The American people need to understand this is about a government takeover of the whole health care system," said Rep. Paul Broun, R-Ga.

The most contentious issue is a new government-run insurance plan that would be offered alongside private coverage within new purchasing marketplaces, or "exchanges," where individuals and small businesses could shop for and compare options.