WASHINGTON - Casting health-care overhaul as a legacy for the American people and failure as politically unthinkable, President Obama yesterday rallied Senate Democrats to deliver on their party's half-century quest to expand the social safety net by providing access for all.

At the Capitol during a rare Sunday session of the Senate, Obama delivered a closed-door pep talk to the fractious Democratic caucus that lasted about 45 minutes. Deep divisions remain over abortion coverage, but there was hope for compromise on whether the government should directly offer health insurance in competition with private companies.

"They're going to get it done," Obama said as he left. He avoided specifics in the meeting with senators and took no questions.

The health-care legislation - Obama's signature domestic policy goal - would provide coverage to more than 30 million additional people over the next decade with a new requirement for nearly everyone to purchase insurance. There would be new marketplaces where people could shop for and compare insurance plans, and lower-income people would get subsidies to help them afford coverage.

The federal-state Medicaid program for the poor would be expanded, and there would be a ban on unpopular insurance company practices such as denying coverage based on medical history.

Senate Majority Leader Harry Reid, D-Nev., who had invited Obama, sounded confident.

Republicans "want this to be, as one senator said, President Obama's Waterloo," Reid told reporters. "And it's not going to be."

White House spokesman Bill Burton said that Obama thanked lawmakers for their work and encouraged them to move ahead on "this historic opportunity." Democrats are keenly aware of former President Bill Clinton's failure to pass health care legislation in 1994, and their repudiation at the polls that November.

Obama said this is "the most significant social legislation in decades - so don't lose it," said Sen. Joe Lieberman, I-Conn. Obama was accompanied by Vice President Joe Biden and other senior administration officials.

Obama "pledged to work with us in any meaningful way that he can," Reid told reporters.

Reid has 58 Democrats and two independents in the Democratic caucus. He may be able to get one or two Republican votes, at the most. He is still short of the 60 votes he needs to shut off debate and move to a final up-or-down vote on the bill.

At Reid's request, moderate and liberal lawmakers are trying to find a compromise on the government insurance plan that could also potentially attract Sen. Olympia Snowe, R-Maine, the one Republican to vote for the Democrats' health bill in committee.

A new idea under discussion involves national nonprofit insurance plans that would be administered by the Office of Personnel Management, which oversees the popular Federal Employees Health Benefits Program.

Snowe called the possible compromise "a positive development" because it would give consumers more options for buying insurance. Underscoring the chase for 60 votes, and the possibility that she could break ranks with the GOP, Obama met with Snowe at the White House on Saturday.

"Progress is being made and that's not just talk," Reid said. After three hours of negotiation last evening, Sen. Charles Schumer, D-N.Y., said that "we're not there yet," but he was encouraged.

At least one moderate Democrat was unpersuaded by Obama's appeal.

Sen. Ben Nelson, D-Neb., objects to Reid's provisions on abortion coverage, to a government insurance plan now in the bill, and to a new long-term care insurance program.

"For those who have made a decision to be supportive, I think [Obama] was persuasive," Nelson said. "There are still issues that have to be resolved."