WASHINGTON, USA (AFP) — US lawmakers closed debate ahead of a contentious but purely symbolic Wednesday vote to repeal President Barack Obama's health care law, as outraged Democrats accused Republicans of seeking to score political points.

Democrats have slammed the effort — the 31st vote to repeal part or all of the Affordable Care Act — as a brash political show, but acknowledged it's all but certain to pass the House of Representatives.

"You're going to win the vote, but you're going to lose the case, and the debate," roared John Dingell, the dean of the House who has served in the chamber since 1955.

"I say shame. You're wasting the time of the American people," he said at the conclusion of more than five hours of debate during which lawmakers made their cases for or against the reforms signed into law in 2010 and upheld as constitutional by the Supreme Court late last month.

Republicans, led by Mitt Romney who is challenging Obama for the White House in the November election, have sought to repeal the law from day one, while most Democrats have praised it as bringing the world's richest nation closer than ever to universal health care for its citizens.

Romney got a taste yesterday of how some US minority voters are reacting to his push to repeal Obamacare when he addressed the National Association for the Advancement of Coloured People (NAACP), America's largest civil rights group.

Attendees to the group's annual convention responded to Romney with loud, sustained boos when he mentioned the repeal, perhaps the most negative reaction to anything he has said on his year-long campaign for the White House.

Republicans say "Obamacare" places unfair financial burdens on small businesses whose costs they say are rising under the law — charges the White House refutes.

"The new harsh reality is that creating new jobs and bringing on new employees may be too expensive and too burdensome if this law is allowed to stand," House Majority Leader Eric Cantor said.

Cantor essentially acknowledged the vote was a bid at political positioning.

The Republican leadership brought the issue to vote "so that we may all be on record following the Supreme Court decision in order to show that the House rejects Obamacare," he said.

"We are committed to taking this flawed law off the books."

With Romney insisting that the law's mandate that all Americans obtain health insurance or pay a fine amounts to a massive tax hike, the issue has morphed into a pivotal campaign battle front.

But the vote is dead in the water. Democrats control the Senate, and the White House has informed Congress that the president would veto the legislation should it reach his desk.

Yesterday's repeal vote illustrates what Americans "loath about politics in Washington," White House spokesman Jay Carney told reporters.

"Casting these votes again and again and again... does nothing to improve the bottom line for middle-class families."

Secretary of Health and Human Service Kathleen Sebelius issued a dire warning about the "devastating effects" that would hit millions of Americans should the Republican repeal come into force.

Ending the law would "take us back to the days when insurance companies were not accountable to anyone," she said in the Minneapolis Star Tribune, citing how repeal could see the re-imposition of lifetime dollar caps on benefits and refusal to cover patients due to pre-existing conditions.

Repeal would also mean an estimated 30 million low-income Americans would lose the health insurance guaranteed them under law, and three million young adults may be dropped from their parents' plans.