WASHINGTON  President Obama said Thursday that he “would love to have more Republicans engaged” in the health care negotiations under way in Congress, but expressed doubt that a bipartisan compromise could be reached because he suspected the party’s leadership was intent on defeating his signature domestic priority.

“I think early on, a decision was made by the Republican leadership that said, ‘Look, let’s not give him a victory,’ ” Mr. Obama said, accusing his rivals of trying to reprise the efforts that went into derailing the Clinton health care agenda.

“There are some folks,” he added, “who are taking a page out of that playbook.”

But one lawmaker who participated Thursday night in a conference call among six Republican and Democratic senators trying to reach bipartisan agreement on a health care plan said the senators agreed to keep working together and asked staff members to focus on making health coverage more affordable while holding down medical costs.

“We are hanging in there,” said Senator Kent Conrad, Democrat of North Dakota, after the telephone conference of almost one hour and 40 minutes. “Is it easy? No. But I tell you, I have never seen a group with a greater sense of purpose than this group.”