“There is not only an economic element to this and a legal element to this, but there is a human element to this,” said the president, who appeared in the Rose Garden, flanked by President Felipe Calderón of Mexico and Prime Minister Stephen Harper of Canada. “I hope that’s not forgotten in the political debate.”

Mr. Obama has not hesitated to challenge the Supreme Court before. In his State of the Union address in 2010, with several stone-faced justices sitting in the audience, he harshly criticized the court’s decision in the Citizens United campaign finance case, saying it would “open the floodgates for special interests — including foreign corporations — to spend without limit in our elections.”

Mr. Obama’s response on health care overshadowed a news conference that touched on trade ties between the United States, Mexico and Canada, and American efforts to help Mexico combat drug-related violence.

The United States, the president said, needed to help Mexico both as a good neighbor and out of self-interest. Rampant drug-related violence south of the border, he said, could have a “spillover effect” on Americans living in or visiting Mexico, and could have “a deteriorating effect overall on the nature of our relationship.”

Mr. Calderón blamed much of the violence on the steady flow of guns from the United States to Mexico. He also disputed that Mexico was alone in its problems, claiming that the rate of homicides per hundred thousand inhabitants in Washington is substantially greater than that of any big Mexican city.

President Obama was in South Korea for a nuclear security summit when the Supreme Court began hearing the health care case. But he followed it closely, administration officials said, reading a summary of the oral arguments on the flight home and discussing the case with his White House counsel.

On Monday, Mr. Obama rejected the idea that the individual mandate could be struck down without crippling the whole law. “I think the justices should understand that, in the absence of an individual mandate, you cannot have a mechanism to insure that people with pre-existing conditions can actually get health care,” he said.