By Adam Liptak

WASHINGTON

The Supreme Court on Monday agreed to hear a challenge to the 2010 health care overhaul law, President Barack Obama's signature legislative achievement, setting the stage for oral arguments by March and a decision in late June as the 2012 presidential campaign enters its crucial final months.

The decision to hear the case prompted confident assertions from each side that it was sure to prevail, and gave rise to calculations about the complicated political impact of possible rulings.

The range of issues the court agreed to address amounted to a menu of possible resolutions: The justices could uphold the law, strike down just its most controversial provision or some or all of the rest of it, or duck a definitive decision entirely as premature.

Whatever the outcome, there is no question that the tensions running through the case - between the 26 states challenging the law and the federal government, and between Obama and the Supreme Court led by Chief Justice John G. Roberts Jr. - are likely to give rise to both a political and constitutional blockbuster.

The court's decision to step in had been expected, but Monday's order answered many questions about just how the case would proceed. Indeed, it offered a road map toward a ruling that will help define the legacy of the Roberts court while focusing renewed political attention on the law that has sharply divided Republicans and Democrats.

The court scheduled 5-1/2 hours of arguments instead of the usual one, a testament to the importance of the case, and the court's ruling a few months later will present opportunities and challenges for the presidential contenders as well as for candidates in the battle for control of Congress.

It is hardly clear, for instance, that a Supreme Court ruling upholding the law would help only Obama, as opponents of the law might redouble their efforts to elect candidates committed to repealing it. And a decision striking down the law might allow Obama to court voters unhappy with the Supreme Court's decisions as he did in cases like Citizens United, which allowed unlimited campaign spending from corporations and unions.

Appeals from three courts had been vying for the justices' attention, presenting an array of issues beyond the central one of whether Congress has the constitutional power to require people to buy health insurance or face a penalty through the so-called individual mandate.

The Supreme Court agreed to hear appeals from just one decision, from the 11th U.S. Circuit Court of Appeals in Atlanta, the only one so far striking down the mandate. The decision from a divided three-judge panel said the mandate overstepped congressional authority and could not be justified by the constitutional power "to regulate commerce" or "to lay and collect taxes."

The appeals court went no further, though, severing the mandate from the rest of the law.

On Monday, the justices agreed to decide not only whether the mandate is constitutional but also, if it is not, how much of the balance of the law, the Patient Protection and Affordable Care Act, must fall along with it.

But even the Obama administration has said that the mandate is "absolutely intertwined" with two other provisions - one forbidding insurers to turn away applicants, and the other barring them from taking account of pre-existing conditions.

In a statement issued soon after the decision, the administration reaffirmed its position that the Constitution permitted Congress to enact the mandate.

"We know the Affordable Care Act is constitutional and are confident the Supreme Court will agree," said Dan Pfeiffer, the White House communications director.

Pam Bondi, Florida's attorney general, said she welcomed the court's prompt action in agreeing to review the 11th Circuit's decision, in which her state was the lead plaintiff.

"Throughout this case," Bondi said, "we have urged swift judicial resolution because of the unprecedented threat that the individual mandate poses to the liberty of Americans simply because they live in this country."

The Supreme Court has not yet decided whether to hear a challenge brought by Virginia Attorney General Ken Cuccinelli.