The U.S. Supreme Court struggled on Wednesday over what to do about President Barack Obama's entire healthcare overhaul should the nine justices decide to strike down as unconstitutional the insurance requirement underpinning the law.

At the end of a 90-minute session, no clear consensus emerged for the fate of the entire law should the justices decide to void its key provision - the mandate that most Americans obtain medical insurance by 2014 or face a penalty.

The court - in the third and final day of historic arguments in the case - is expected issue a ruling by late June.

The four liberal justices were skeptical about tossing out the sweeping law that has hundreds of other provisions aimed at stemming soaring healthcare costs and expanding coverage - some of which are already in effect.

Chief Justice John Roberts, leader of the conservative five-member wing of the court, questioned how they could discern the intent of Congress when it dually titled the law "Patient Protection and Affordable Care Act."

And one of the other conservatives on the court, Justice Antonin Scalia, made clear that he believed if the justices strike down the individual mandate, the entire law must go. "My approach would be if you take the heart out of the statute, the statute is gone."

Justice Anthony Kennedy, considered the swing vote on the court, voiced concern about the cost risks to insurance companies if the mandate - which would bring millions of healthy young people into the healthcare system and spread out costs - is invalidated alone.

(Reporting By James Vicini and Joan Biskupic; Editing by Howard Goller and Will Dunham)