Portland, Maine (Reuters) - He didn't mention them by name, but they seemed to be on his mind. President Barack Obama defended his healthcare reform effort on Friday without mentioning the Supreme Court justices who hold the law's fate in their hands.

Obama's healthcare legislation, considered his signature domestic policy achievement, dominated headlines this week as the Supreme Court heard arguments about its constitutionality.

The president was briefed about the proceedings but did not comment on healthcare publicly until Friday, during a series of fund raisers for his re-election campaign in Vermont and Maine.

While listing the reform as evidence of the change agenda he promised in 2008, Obama skirted the issue of the Supreme Court's potentially game-changing role.

Change is the health care reform that we passed after over a century of trying, he said to applause from a crowd of donors at a campaign event in Burlington, Vermont.

Already millions of seniors are paying less for their prescription drugs because of this law. Already, Americans can't be denied or dropped by their insurance company when they need care the most. Already, they're getting preventive care that they didn't have before. That's happening right now.

Republican presidential candidates have made repealing what they call Obamacare a key promise of their respective quests to win their party's presidential nomination and challenge Obama in the November 6 election.

The Supreme Court could help their case and deliver a major blow to the president if it nixes all or part of the law in a decision expected by late June.

The justices held closed-door deliberations about the law on Friday and were likely to have cast preliminary votes.

Obama highlighted healthcare reform as one of his top accomplishments at a second series of fund raisers in Maine on Friday. Ticket prices for the final fundraising event started at $5,000.

(Editing by Todd Eastham)