WASHINGTON — The Obama administration defended the health care overhaul in a filing Friday with the Supreme Court that calls the law an appropriate response to a "crisis in the national health care market."

The administration filed a written submission in the high court's biggest case this term, with the potential to affect President Barack Obama's bid for re-election.

The government called on the court to uphold the core requirement that individuals buy insurance or pay a penalty. One federal appeals court struck down the so-called individual mandate as exceeding Congress' power under the Constitution. But two other federal appeals courts upheld the law and agreed with the administration's argument that Congress was well within its power to adopt that requirement.

Florida and 25 other states, as well as the National Federation of Independent Business, told the court in separate briefs that if the justices strike down the individual requirement, they should invalidate the rest of the law as well. Thirty-six Republican senators echoed the states' argument in their own filing.

The law is aimed at extending health insurance coverage to more than 30 million previously uninsured people and would, by 2019, leave just 5 percent of the population uninsured, compared with about 17 percent today, according to the Congressional Budget Office. About half of the increase would come from the individual requirement; the rest would come from an expansion of Medicaid and other provisions.

The health care law has attracted intense opposition from Republicans, including the party's presidential candidates, all of whom have vowed to repeal it if elected. The individual insurance requirement has been a particular lightning rod because it forces people to buy a product from a private insurer whether they want to or not, or pay a penalty for failing to do so.