WASHINGTON — President Barack Obama's administration Wednesday asked the US Supreme Court to rule on his landmark health reforms, seeking to halt a flurry of conservative legal assaults on the new law.

Health care reform passed in 2010 fulfilled decades of Democratic dreams but was fiercely contested by Republicans, and the legislation is likely to emerge as a key issue in the run-up to the 2012 presidential election.

"We know the Affordable Care Act is constitutional. We are confident the Supreme Court will agree. We hope the Supreme Court takes up the case and we are confident we will win," said Stephanie Cutter, a top Obama advisor.

The administration will ask the Supreme Court to declare the key provision of the new law, requiring everyone to buy health insurance by 2014 if they can afford it, constitutional.

Republican opponents of the law say the government has no power to compel people to act to buy health insurance and have vowed to repeal the law in the courts and eventually replace it through new legislation.

But Cutter argued that such a view was "simply wrong" because people who do not buy insurance do not "opt out" -- but hurt everyone else because taxpayers end up subsidizing their care when they are taken to emergency rooms.

"Those costs -- $43 billion in 2008 alone -- are borne by doctors, hospitals, insured individuals, taxpayers and small businesses throughout the nation," she said in a White House blog post.

The White House also justifies the individual mandate by saying that without it, people would wait until they get sick to apply for coverage, which would cause insurance premiums for everyone to rise.

"We don't let people wait until after they've been in a car accident to apply for auto insurance and get reimbursed, and we don't want to do that with health care," Cutter said.

The White House move came after 26 states and small businesses earlier called on the Supreme Court to strike down the totality of Obama's reform.

Their action followed an August ruling by the Eleventh Circuit appeals court, based in Atlanta, that the individual mandate exceeded Congress's powers.

But the court ruled that the remainder of the health care law, which extended coverage to an extra 32 million people and was a long-held dream of Democrats, was within the bounds of the Constitution.

A number of other courts have struck down challenges to the law, making it inevitable that the Supreme Court would eventually be called upon to judge the law, possibly in 2012 amid the political heat of Obama's reelection campaign.