Obama's landmark health care overhaul moved toward a vote in the House Saturday after anti-abortion lawmakers won a chance to knock out language that would let people who get federal subsidies buy insurance plans that include abortion coverage. Democratic leaders were hopeful they could pass the bill, giving Obama his biggest victory since last November's historic election, no matter how the abortion issue is decided. Obama made a rare Saturday visit to Capitol Hill in an effort to cement a majority to pass the legislation that is certain to be seen as a test of his presidency.

Abortion-rights supporters were outraged at the concession to abortion opponents. Rep. Diana DeGette, D-Colo., said "there is a risk" that some in the Pro-Choice Caucus would vote against the bill as a result.

The bill would cost more than $1 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.

Republicans were united in their opposition to the bill, using procedural delays to slow the debate.

"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 in the 10-year, $1.2 trillion House bill 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.

The abortion agreement was reached at midnight Friday after hours of intense negotiations brokered by House Speaker Nancy Pelosi, D-Calif. Democratic Reps. Bart Stupak of Michigan, Brad Ellsworth of Indiana and other abortion opponents fought for and won an opportunity to insert tougher restrictions into the legislation during debate, despite fervent opposition from pro-choice liberals who are a driving force behind the overall bill.

"We wish to maintain current law, which says no public funding for abortion," Stupak said.

Federal law currently prohibits the use of federal funds to pay for abortions except in cases of rape, incest or situations in which the life of the mother is in danger. Left unresolved is whether individuals would be permitted to use their own funds to buy insurance coverage for the procedure in the federally backed insurance exchange envisioned under the legislation.

Stupak's amendment would deny abortion coverage to anyone who gets federal insurance subsidies or buys a policy from the government. People could buy separate policies covering just abortions using their own money.

DeGette called Stupak's amendment "the biggest restriction on a women's right to chose that's been considered on the floor of the House" in her 13 years in office.

The leadership's hope is that no matter how the vote on the abortion measure turns out, Democrats on both sides of the abortion divide will then unite to give the health care bill a majority over unanimous Republican opposition.

With Democrats' command of the necessary votes looking tenuous, Obama threw the weight of his administration behind the effort to round up support. He and top administration officials worked the phones to pressure wavering lawmakers.

Rep. Jason Altmire, D-Pa., said he heard from Obama, White House Chief of Staff Rahm Emanuel, Health and Human Services Secretary Kathleen Sebelius and Education Secretary Arne Duncan.

Their message: "This is a historic moment. You don't want to end up with nothing," said Altmire, who remained undecided.