WASHINGTON  President Obama exhorted Senate Democrats on Sunday to put aside their differences and seize their moment in history by passing landmark health legislation. But senators said he did not mention sticky issues like abortion or a new government-run insurance plan.

Though Mr. Obama gave them no guidance on the question, Senate Democrats on Sunday intensified their yearlong effort to build consensus around some form of a public insurance plan to compete with private insurers.

The Senate majority leader, Harry Reid, Democrat of Nevada, named 10 senators  five centrists and five liberals  to seek a compromise. Under a leading proposal, the federal Office of Personnel Management would negotiate with insurers to offer one or more national health plans to individuals, families and small businesses. The personnel office has decades of experience arranging health benefits for federal employees, including members of Congress.

The push for a deal on the public option indicated the pressure Democrats were feeling to resolve their differences if they hope to pass the bill by their self-imposed deadline of Christmas. On Monday, the Senate plans to take up another explosive issue, restrictions on insurance coverage for abortion.