WASHINGTON -- At 7 o'clock this morning, the Senate plans to push landmark health care legislation over the finish line with the last in a string of midnight and daybreak votes capping months of infighting and procedural delays.

And with that, the hardest work of all will begin: reckoning with long-standing differences with the House and uniting behind a single bill that can be sent to the president.

Democrats already are outlining a strategy to achieve a final compromise that can satisfy the more liberal House without upsetting the painstakingly assembled coalition of 60 Senate Democrats and independents.

Central to those talks, House leaders said, will be the search for an acceptable substitute for a government-run insurance plan that those without medical coverage could purchase, a provision the House designed to compete with private insurers and force them to rein in costs.

While the Senate has decisively rejected the "public option," House leaders said they will demand other concessions to ensure that Americans can afford the insurance they will be required to buy if the bill becomes law.

"We have to be absolutely convinced that this is going to accomplish the goal of holding down the cost of health insurance. The American consumer cannot be left hostage to the whims of private insurance," said Rep. Chris Van Hollen, D-Md., a member of the House leadership.

"We're asking every American to share some responsibility in getting health insurance; we need to ensure that every American can afford it," he said.

House Speaker Nancy Pelosi, D- Calif., has signaled approval for the Senate's solution: the creation of at least two nationwide insurance plans run by private companies but overseen by the Office of Personnel Management, the same federal agency that handles health insurance for members of Congress.

In a conference call Wednesday, Pelosi also assured rank-and-file Democrats that they would not be asked to rubber-stamp the Senate bill and began soliciting ideas to improve it.

Among the options under discussion: pressing the Senate to increase the federal subsidies that would be offered to low- and middle-income people who do not have access to affordable coverage through an employer.

Also, having a single, national marketplace for people buying insurance, rather than 50 separate state-based exchanges the Senate prefers. And moving up the launch date of those marketplaces and subsidies to 2013, one year earlier than under the Senate bill.

With Democrats racing to finish work in time for President Barack Obama's first State of the Union address in late January or early February, those changes promise to increase the cost of the $871 billion Senate package, which already is bumping up against the $900 billion cap Obama set earlier this year.

"The tension is, the more you move toward the House bill, the more you have to pay for that," said Drew Altman, president of the Kaiser Family Foundation. "There isn't a lot of wiggle room financially, and there isn't a lot of wiggle room politically in any of this."

Other contentious issues also must be resolved in talks between the two chambers, including how to handle abortion coverage and whether to permit undocumented immigrants to use their own money to buy insurance on the exchanges.

The House and Senate also differ on which taxes to raise to pay for the most dramatic expansion of insurance coverage since the 1965 creation of Medicare, and how to enforce nearly $500 billion in proposed payment cuts to Medicare providers, another major source of financing.

The outlines of a compromise might be emerging on the financial issues. Obama said Wednesday that he expects the Senate's tax on high-cost insurance policies to be included in the final bill, despite persistent opposition in the House and among labor unions, who have bargained away wages for better coverage over the years.

Economists said the "Cadillac tax" promises to control health costs by encouraging people to purchase less luxurious coverage.

House leaders have proposed a surtax on millionaires, but aides said they may settle for an expanded version of the Senate's proposal to raise the Medicare payroll tax on annual income over $200,000 for individuals and $250,000 for families, a less confrontational approach to taxing the wealthy.

The White House also has endorsed the Senate's plan to create an independent advisory board with broad powers to cut Medicare spending. Territorial House leaders are reluctant to relinquish congressional authority over the federal health program for retirees, but aides say they may ready to broker a deal there as well.

Pelosi and Senate Majority Leader Harry Reid, D-Nev., plan to talk next week about how to move forward, with the most likely course being informal negotiations rather than a formal conference committee. That would give negotiators more flexibility to come up with new policies in service of a compromise, and eliminate some complicated procedural obstacles.

Negotiators from both chambers could rewrite the Senate bill and send it to the House for a vote. The Senate then would give it final approval.

Pelosi has asked key House chairman to return to Washington the first week in January to launch that effort, with the full House due back a week later. The Senate is out until Jan. 19, leaving little time to push through a final bill.

Senate Republicans have vowed to fight the Senate bill with every parliamentary weapon they can muster.