Debate is under way in the US House of Representatives on a healthcare reform bill at the heart of President Barack Obama's domestic agenda.

美国众议院正在就奥巴马总统提出的国内头等大事——医疗改革方案进行激烈讨论。

Democrats¹ have spent days trying to win support for the reforms" width="226" height="170" src="/upimg/100322/4_024114_1.jpg" />
Senior Democrats have spent days trying to win support for the reforms

A vote on the final passage of the bill is expected to be very close, with no Republicans supporting the measure.

Senior Democrats believe they have the 216 votes needed to pass the bill, after days of negotiations² to persuade wavering（摇摆的） party members to back it.

If passed, the measures would extend health coverage³ to 32m more Americans.

On the floor of the House, Republicans and Democrats have been arguing fiercely over procedural issues governing the terms of the debate.

The first hurdle⁴ towards approving the reforms was cleared when the House voted by 224 to 206 to pass a set of rules governing the debate.

Lawmakers are expected to hold two more key votes, one on a Senate version of a health reform bill and one on a package of changes that would be made to that bill.

Speaking before the debate, Democratic House Caucus⁵ leader John Larson said: "We have the votes. We are going to make history today."

House Speaker Nancy Pelosi, who was heckled（激烈质问） by anti-reform demonstrators on her way to the Capitol, said: "We are doing this for the American people."

In a move designed to win the support of a bloc⁶ of anti-abortion⁷ lawmakers, Mr Obama on Sunday announced he plans to issue an executive order assuring that healthcare reform will not change the restrictions⁸（限制） barring federal money for abortion.

The Republicans are unanimously（全体一致地） opposed to the legislation, which they say is unaffordable and represents a government takeover of a large part of the country's economy.

Senior House Republican Mike Pence told CNN he was doubtful the Democrats did have the votes needed to approve the bill and said his party would do whatever it could to prevent its passage.

Eric Cantor, the second-ranking Republican in the House, told ABC: "The American people don't want this to pass. The Republicans don't want this to pass. There will be no Republican votes for this bill."

If all three votes are passed in the House, Mr Obama will be able to sign the legislation into law.

Democratic Senate Majority Leader Harry⁹ Reid assured House lawmakers on Saturday he had the "commitment of a significant majority" in the Senate to ensure the package of changes the House wants to its bill will pass there.

The BBC's Richard Lister in Washington says that whatever happens, this will be a significant day in American politics.

Either healthcare will be significantly reformed, he says, or reform will be kicked into the long grass for perhaps decades to come - which could have all kinds of budgetary implications（财政预算的影响） for the future, as the US cannot afford to continue on its existing track.

If passed, the reforms will deliver on Mr Obama's top domestic priority by providing insurance to some 32 million of the Americans who currently lack coverage.