President Obama challenged the Supreme Court on Monday to uphold his administration’s sweeping health-care reform legislation, arguing that overturning the law would amount to an “unprecedented, extraordinary step” of judicial activism.

In his first public comments since the court wrapped up oral arguments last week in its review of the 2010 law, Obama questioned the authority of the nine-member panel of unelected justices to reverse legislation that was approved by a majority vote in Congress.

Obama made his argument in unusually blunt language that was rare for a sitting president during a pending case, emphasizing the high stakes in an election year and signaling that the White House might seek to turn a loss in the high court into a campaign issue aimed at rallying the president’s liberal base.

“I’d just remind conservative commentators that for years what we’ve heard is, the biggest problem on the bench was judicial activism or a lack of judicial restraint — that an unelected group of people would somehow overturn a duly constituted and passed law,” Obama said during a Rose Garden news conference. “Well, this is a good example. And I’m pretty confident that this court will recognize that and not take that step.”

During the high court’s three-day review of the law, which requires uninsured Americans to purchase health-care coverage, justices on the right appeared at least open to declaring the heart of the legislation unconstitutional. Such a ruling would represent a major blow for Obama, who has counted health-care reform among the most consequential domestic policy achievements of his presidency.

The future of “Obamacare” has become a major issue on the campaign trail with Republicans accusing the president of government overreach on the sharply partisan issue of how to provide coverage to millions of uninsured Americans.

Yet despite the high stakes, White House officials have refused to acknowledge whether they are planning for contingencies in the case of a loss when the court announces its decision in June. Senior administration officials declined to lay out potential options in a briefing for reporters Monday morning.

Asked about a Plan B, Obama said: “I’m confident that this will be upheld because it should be upheld. That’s not just my opinion; that’s the opinion of a whole lot of constitutional law professors and academics and judges and lawyers who have examined this law, even if they’re not particularly sympathetic to this particular piece of legislation or my presidency.”

Though past presidents have occasionally inveighed against judicial activism, legal analysts and historians said it was difficult to find a historical parallel to match Obama’s willingness to directly confront the court.

Barbara Perry, a senior fellow at the University of Virginia’s Miller Center for presidential history, said that after the Supreme Court voided 16 pieces of New Deal legislation in 1936, President Franklin D. Roosevelt waited until after he had been re-elected to attack the court.

“The reason presidents are reluctant to take on the court is because they are a co-equal branch of government, they have lifetime tenures and they can be very powerful in their own way,” Perry said. “I would contrast that with Obama’s willingness to take on the court.”

She noted that Obama complained during his 2010 State of the Union address of the court’s decision that year in the Citizens United case, ruling that the First Amendment prohibited the federal government from restricting political expenditures by corporations.

With the robed justices seated in the front row of the House chambers, Obama said that the court “reversed a century of law” to “ open the floodgates for special interests” to influence elections.

“That he called them out in the State of the Union address shows he’s not squeamish about making a face-to-face attack on them,” Perry said.

Obama was asked about the health-care law during a joint news conference with Canadian Prime Minister Stephen Harper and Mexican President Felipe Calderon, after the three leaders met at the White House for a North American summit.

Obama emphasized the costs associated with overturning a law that his administration already has begun to implement. He said 2.5 million young people have coverage who otherwise would not and tens of thousands of Americans with preexisting conditions also are covered by insurance thanks to the legislation.

Thirty million more Americans stand to benefit once the law is fully implemented by 2014, Obama said.

“So there’s not only an economic element and a legal element, but a human element to this,” Obama said. “Hopefully, that’s not forgotten in this political debate.”