President Barack Obama defended his signature health care reform Friday, without discussing a Supreme Court case that could spell its end ahead of November's presidential elections.

Reprising the "change" theme of his successful 2008 campaign for the presidency, Obama said "yes, change is the that we passed after over a century of trying."

He said the law was "reform that will finally ensure (that) in the United States of America, no one will go broke just because they get sick."

"Already, 2.5 million young people now have health insurance that they didn't have before because this plan lets them stay on their parents' health plan. Already, millions of seniors are paying less for their because of this law," the president said before some 4,500 people gathered at the University of Vermont.

"Already, Americans can't be denied or dropped by their insurance company when they need care the most. Already, they're getting that they didn't have before. That's happening right now."

The future of the reform enacted two years ago after fierce battles in Congress is now in the hands of the Supreme Court, divided between five conservative justices nominated by Republican presidents and four nominated by Democratic presidents.

During hearings this week, the justices cast doubt over the law's linchpin requirement mandating that nearly every American must be insured, giving hopes to critics of the reform looking to see it repealed.

The court is due to make a ruling in late June, just four months before in which Obama is seeking a second term.

The White House says it remains confident about the constitutionality of the law.