President Barack Obama's administration asked the US Supreme Court to uphold his historic health care law, likely sparking an explosive legal showdown in the heat of the 2012 election.

The legislation, passed in 2010, fulfilled decades of Democratic dreams of social reform, but was fiercely contested by Republicans, and the law is likely to emerge as a key issue as Obama seeks reelection next year.

"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 Justice Department asked the 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 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 called on the Supreme Court to strike down the totality of Obama's reform.

The petitioners also asked for a swift Supreme Court judgement, saying the "grave constitutional questions surrounding the ACA and its novel exercises of federal power will not subside until this court resolves them."