WASHINGTON -- President Barack Obama and a divided Congress have 18 days to figure out whether to continue a Social Security payroll-tax cut, avoid a huge drop in Medicare payments to doctors and maintain many unemployment benefits.

But on Tuesday, no one knew where the two warring parties could find common ground.

"I don't know how this will come out. I honestly don't. It's like a book that is almost written, but we don't know how the final chapter comes out," said Sen. Ben Nelson, D-Neb.

The House landed the latest partisan blow Tuesday, voting 234-193 for a GOP package that most Democrats abhor. The Obama administration said it "strongly opposed" the bill.

"This debate should not be about scoring political points. This debate should be about cutting taxes for the middle class," the White House said.

Three major programs face changes Jan. 1 unless lawmakers reach a deal. They include:

--Social Security tax: Employees currently pay a tax of 4.2 percent on wages up to $106,800, 2 percentage points below the 2010 level. The tax is scheduled to revert to 6.2 percent on Jan. 1, which workers will pay next year on the first $110,100 of wages. The House GOP bill would extend the 2-point break for 2012. Obama favors that, but he opposes how the Republicans would pay for it.

--Medicare: Under current law, Medicare payments for physician services will drop 27.4 percent in January. The House Republican bill would rescind the drop and allow reimbursement rates to go up 1 percent next year and again in 2013.

--Unemployment insurance: Regular benefits are available for up to 26 weeks, but in states with high unemployment rates, the jobless can receive more aid. Currently, authority for a total of 99 weeks expires at the end of the year, and an estimated 2.1 million people could lose benefits through mid-February. Republicans would gradually reduce the maximum number of weeks to 59.

The most divisive issue involves how to pay for all this. Democrats want a surtax on millionaires. Republicans hate that; they want spending cuts, notably by extending a freeze on civilian federal pay.

The next step is expected to be a Senate vote on the House plan by Thursday. Since Democrats control 53 of the 100 seats, the bill will probably fail, setting up negotiations. Somehow, a resolution is expected to emerge.

Obama has said he's prepared to stay in Washington through the holidays if necessary.