Bipartisan negotiators were closing in on budget deal Tuesday, although the talks remain delicate and sources familiar with the haggling were hesitant to predict that an agreement would be reached before Congress adjourns for the year.

Senate Budget Committee Chairman Patty Murray, D-Wash., and House Budget Committee Chairman Paul Ryan, R-Wis., could shake hands on a two-year federal spending plan as soon as Tuesday evening, with a vote in the Republican controlled House coming as early as Thursday. But first, the two top negotiators must iron out final differences over how to replace a portion of the automatic spending cuts, known as the sequester, with budget savings.

Then, the budget blueprint would have to be vetted with Democrats and Republicans in the House and Senate to see if it has the votes to clear each chamber. Ryan briefed House Republican leaders on the negotiations Tuesday afternoon, and it is possible that he might discuss the budget plan with the full GOP conference on Wednesday.

"Last night, Congressman Ryan returned to Washington,” his spokesman, William Allison, said. “He is still working with Senator Murray to cut spending in a smarter way. They haven't reached an agreement yet. We have nothing new to confirm at this time."

Murray declined to answer reporters’ questions following the Senate Democrats’ weekly, closed-door caucus lunch. But Senate Majority Whip Dick Durbin, D-Ill., sounded optimistic that a deal was within reach, although he alluded to potential sticking points. Durbin declined to elaborate.

“I think we’re close,” Durbin told reporters. “I think there is a positive feeling.”

The Senate is scheduled to be in session next week. But Republican leaders are bent on adjourning the House on Friday, as they have long planned, meaning any deal must be struck by Wednesday to allow a vote this week. House GOP leaders are not inclined to wave the three-day rule they implemented for legislation requiring that it be available for viewing online for three calendar days prior to a vote.

The crux of any deal involves eliminating some of the sequester-driven budget cuts and to increase overall spending beyond the $967 billion cap set by the sequester. This additional spending, in the neighborhood of $35 billion, would be divided between the domestic programs Democrats want to spare and the Pentagon, which Republicans want to protect.

At issue is where the budget savings comes from to pay for this. Democrats are reluctant to cut spending elsewhere and Republicans are opposed to tax increases. Murray and Ryan have attempted to bridge the gap with a proposal to increase government fees and other budget savings. Democrats and Republicans are uncomfortable with different aspects of the budding agreement, and one Republican lobbyist said it is unlikely to clear the House unless 100 Democrats back it.

The high-water mark for GOP votes on the deal under discussion, according to this source, is about 140 votes. A stronger Republican vote total also is possible, according other GOP insiders monitoring the negotiations. Most Senate Republicans are likely to reject the proposed deal, because it would bust the sequester-set spending cap. But Senate Democrats are expected to deliver sufficient votes to ensure that any agreed-upon deal passes.

If the Murray-Ryan compromise falls apart, House Republicans could put a short-term continuing resolution budget bill on the floor to ensure the government doesn’t shut down on Jan. 16, when the current temporary funding measure runs out. The latest stopgap measure would set funding at the $967 billion sequester levels and could be ready for a vote by Friday or immediately after Congress returns from the holiday break in January.

“It’s going to be hard to get an agreement that’ll be popular,” said Sen. Jeff Sessions, of Alabama, the top Republican on the Senate Budget Committee.