With negotiations over a massive $1.1 trillion budget package moving at a glacial pace, GOP leaders are now openly predicting that Congress will blow past a Dec. 11 deadline for funding the federal government.

Both sides appear to be notching wins in the high-stakes talks. Republicans are confident they'll be able to lift a ban on exporting crude oil, though the GOP is wary of acceding to Democratic demands on environmental policy in return for allowing such sales. Democrats are relieved Republicans aren't fighting to strip funds from Planned Parenthood.

One major open question is how Congress will handle the Syrian refugee crisis, and whether the issue gets caught up in the year-end spending fight. The House will vote Tuesday to tighten restrictions on visa-free travel by visitors to the U.S. GOP leaders privately hope that the vote will take pressure off them to include additional certifications for Syrian and Iraqi refugees to the U.S. in the must-pass spending bill. President Barack Obama and Democrat have strongly opposed inclusion of any refugee language in the omnibus bill.

Yet there are still big disputes between the two parties over environmental policy provisions, including global warming and clean water programs. The disagreements have Democrats vowing to oppose the omnibus package in its current form. Furthermore, Republicans are planning to go it alone on a massive, two-year package of popular tax breaks, known as extenders, after talks all but broke down with Democrats.

The current government funding bill expires on Friday, but Speaker Paul Ryan (R-Wis.) and House Majority Leader Kevin McCarthy (R-Calif.) said an agreement is unlikely by then.

"When it comes to the [omnibus], I'm seriously looking at having us in on Friday or over the weekend to get our work done," McCarthy said during a press conference on Monday. The California Republican said he did not anticipate any problem passing a stopgap spending bill to keep federal agencies open beyond Friday.

Top Republicans have vowed they won't allow a government shutdown; the last one, in 2013, was seen as a debacle for the party. Yet bitter policy fights are delaying a deal.

“We thought we had an agreement. And we’re moving very substantially through the weekend," said Sen. Barbara Mikulski, the top Democrat on the Appropriations Committee. "But … complications with the tax extenders have been a bit of a setback. But we were making great progress on the money and I felt great progress on the [policy] riders. Right now we seem to be stuck.”

House Ways and Means Chairman Kevin Brady (R-Texas) told reporters that he expected to release a two-year tax extenders proposal on Monday evening.

The tax-extender package and the spending bill are the final major two items Congress needs to complete before the end of the year, and the negotiations over them have become intertwined. House Minority Leader Nancy Pelosi (D-Calif.) said Democrats will oppose both packages as they are currently drafted.

"Following our Caucus and Whip meetings last week, it was clear that Democrats cannot support an omnibus that includes the poison pill riders inserted by the Republican leadership. Furthermore, there is very little support for the tax extenders bill as written. There is also strong opposition to any thought of combining these bills," Pelosi wrote in a letter to fellow Democrats.

"On the omnibus bill, House Democrats accepted the Republican budget number. We accepted how they decided to distribute the funds from the budget agreement. In order for us to support the omnibus bill, the poison pill riders must go."

Democrats on Capitol Hill and the White House are using the threat of a shutdown as leverage against Republicans during the budget and tax talks, knowing that neither Ryan nor Senate Majority Leader Mitch McConnell (R-Ky.) want to risk their majorities by allowing one to occur. Democrats can maximize their negotiating leverage by keeping their rank-and-file lawmakers in line, backed up by a veto threat from President Barack Obama.

Yet there's a limit on how far Democrats and the White House can push Ryan and McConnell. If the Republican leaders run out of patience, they could put a "clean" funding bill on the floor that funds government operations at the previously agreed-upon levels — and rely on GOP votes, plus a handful of Democrats, to pass it. Even if Hill Democrats complained, Obama would likely sign such a measure to avoid a shutdown.

Ryan and McConnell would be loathe to take such a step, however, and senior House and Senate GOP aides vow a budget deal will come together.

A Democratic aide said the party is resigned to the near-certainty that a short-term funding bill will be needed to avert a shutdown on Friday. But Democratic leaders are adamant that they won't accept an extension that goes longer than a week.

"There is no stomach for it," the staffer said.

The dispute over Syrian refugees has been among the most acrimonious. With GOP presidential candidates demanding stricter controls on refugees, Republican leaders in Congress have worked to include a provision in the budget calling for increased federal scrutiny of entrants from the war-torn country. Obama has pledged to allow 10,000 Syrian refugees to resettle in the United States.

Although the House passed a bill recently to tighten controls on Syrian refugees, the White House and top Democrats have strenuously objected to including refugee language in the spending bill. And Republican leaders are slowly starting to acknowledge that it may not be possible to include it in the omnibus package.

As what some Republicans are privately calling a "safety valve," language addressing the visa waiver program may be included instead.

“I think that’s going to be dealt with in the omnibus, is my understanding," Senate Majority Whip John Cornyn (R-Texas) said, referring to visa waiver language.

Lauren French and Seung Min Kim contributed to the report.