Administration attorneys, in court filings and at a briefing, said Congress was within its constitutional powers in requiring Americans to buy insurance by 2014 or pay a penalty, a centerpiece of the law known as the individual mandate.
The law's opponents have argued that Congress overstepped its authority and have raised the hypothetical question of whether Congress next could require that all Americans eat broccoli because of the nation's obesity crisis.
The Supreme Court has scheduled three days of oral arguments in the legal battle for March 26-28, with an election-year ruling expected by the end of June.
The law, Obama's signature domestic policy achievement, seeks to provide health insurance to more than 30 million previously uninsured Americans. His prospective Republican presidential opponents all have strongly opposed the law.
A Supreme Court ruling striking down the law would be a major political and legal setback for Obama ahead of the election, while a decision upholding it would be vindication. Polls show Americans deeply divided over the law.
A senior administration official, who declined to be identified, told reporters that Congress, in adopting the law, responded appropriately to a national crisis after years of debate.
The broccoli hypothetical has "no relevance to the case at hand," the official said, maintaining that the insurance purchase requirement was "not the same" as mandating that people eat or buy broccoli.
The healthcare law has been challenged by 26 of the 50 states and by an independent business group as an unprecedented move by Congress that exceeds its constitutional powers.
The states involved in the challenge, in a Supreme Court brief, on Friday said the entire law, which President Barack Obama signed in March 2010, should be struck down.
"The individual mandate is the centerpiece of the entire federal healthcare act," said Attorney General Pam Bondi of Florida, a state that has led the legal challenge.
"If the court removes the individual mandate, the main hub of the act, the entire healthcare law must be invalidated."
The administration's arguments in its brief backing the law largely mirrored those previously made in its initial appeal to the Supreme Court filed at the end of September.
The attorneys said the law was an attempt by Congress to address a crisis in the national healthcare market, capping nearly a century-long effort to expand access to healthcare by making affordable health insurance more widely available.
They cited statistics showing that healthcare accounts for 17% of the nation's economy and argued that the law was a valid exercise of Congress's power under the Constitution to regulate economic activity affecting interstate commerce.
The brief also cited a law that Massachusetts adopted in 2006 when Mitt Romney was governor. Romney is the frontrunner for the Republican presidential nomination to face Obama in the November elections.
The brief said Congress cited the Massachusetts law as a model for key provisions, including the provision requiring that individuals purchase insurance or pay a tax penalty.
Opponents of the law also filed briefs with the Supreme Court on Friday.
The conservative American Center for Law and Justice filed a brief on behalf of 117 Republican members of the U.S. House of Representatives and 100,000 of the center's supporters urging the justices to declare the entire law unconstitutional.
Thirty-six Republican U.S. senators said in a separate brief the entire law must fall if the individual mandate is struck down.
The Supreme Court cases are National Federation of Independent Business v. Sebelius, No. 11-393; U.S. Department of Health and Human Services v. Florida, No. 11-398; and Florida v. Department of Health and Human Services, No. 11-400.
For National Federation of Independent Business: Michael Carvin of Jones Day.
For Sebelius and the Department of Health and Human Services: Donald Verrilli Jr, Solicitor General of the United States.
Last Updated: 2012-01-09 11:32:26 -0400 (Reuters Health)
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