At a brief news conference after the caucus meeting, Mr. Reid refused to answer questions. He said: “This is like a steeplechase race. The last big puddle is in front of us.”

Senator Tom Harkin, Democrat of Iowa and chairman of the health committee, appeared to be laying the groundwork for a decision to abandon the Medicare buy-in.

“There is enough good in this bill that we ought to move it” even without the Medicare buy-in, Mr. Harkin said. Among the most important provisions of the bill, he said, are stringent new federal regulation of health insurance and coverage for a wide range of preventive health services.

Senator Evan Bayh, Democrat of Indiana, said, “If dropping the Medicare expansion is necessary, that’s what should be done.” He reported that “there was some disappointment by some members that some of the provisions could not be retained.”

The idea of expanding Medicare to cover younger members of the public ran into trouble this weekend when Senator Joseph I. Lieberman, the Connecticut independent, said he would not vote for that proposal. Given the need for Democrats to keep Mr. Lieberman in the fold, Democrats sought to find ways to ease his objections. Mr. Lieberman and Senator Ben Nelson, Democrat of Nebraska and another potential Democratic defector, were both in the private meeting but did not speak, lawmakers said.

Senator Arlen Specter of Pennsylvania, who switched parties earlier this year to become a Democrat, urged his colleagues not to let obstructionists stand in the way. “I came to this caucus to be your 60th vote,” he said to a round of applause, according to observers. Democrats need 60 votes to pass the health care bill over Republican objections.