To give themselves extra time, senators voted to extend government funding, which officially runs out Friday, through next Wednesday. House members are expected to do the same hours before the deadline.
House Appropriations Committee Chairman Hal Rogers of Kentucky said the talks had moved "a few inches."
At the same time, some lawmakers were upbeat that they would complete action by the middle of next week and leave for their winter holidays.
"I think the goal is to wrap things up by Wednesday evening," said a smiling Sen. John Cornyn of Texas, the No. 2 Senate Republican who earlier gently chided a gaggle of reporters who surrounded him. "We're going to get it done. Everything will be alright."
But Rogers wasn't as optimistic and admitted that even getting the bill through with the new Wednesday deadline will be tight because House Speaker Paul Ryan has pledged that the measure has to be public for three days so members can review it before a House floor vote.
Ryan justified extending the deadline and deliberately distanced himself from the massive spending package, saying Thursday, "this is something I more or less inherited from the last regime, and I don't want to rush things through here."
Louisiana Republican Rep. John Fleming told reporters he was glad leaders decided to extend the negotiations into next week.
"We're not going to let a deadline be our enemy in this. We're not going to let Democrats jam us with hard deadlines -- these are all artificial deadlines. We can stay in session all the way through Christmas."
Even though the new deadline is Wednesday, Ryan suggested that was a moving target if negotiations stalled.
"I don't think it would be right to say what date we're going to be done by because I want to make sure that these negotiations are done well and done right, and not by some arbitrary deadline," Ryan said.
In the meantime, both sides were pressing for inclusion of key policy "riders" in the package, which is made up of a $1.1 trillion spending bill and nearly $900 billion tax package. Many are politically charged provisions lawmakers want in the legislation because they otherwise might not get through both chambers of Congress or signed by the President.
For instance, House Democratic Leader Nancy Pelosi said she would "insist" the bill include a provision lifting a ban on Centers for Disease Control and Prevention research of gun violence, something many Republicans oppose.
"With 30,000 gun deaths every year, America is in the middle of a public health epidemic," Pelosi said. "Therefore, I call on the omnibus negotiators to remove the outrageous ban on federal research on gun violence."
But a source close to the negotiations told CNN the Democrats' new push to include the language on gun research wasn't part of the talks up until Thursday, so the public push was viewed as a sign that both sides still had a lot of outstanding issues to resolve rather than coming closer to a deal.
Republicans are pushing to tighten up restrictions on Syrian refugees coming to the United States.
Rep. Jim Jordan, the chair of the conservative House Freedom Caucus, wants to require the secretary of Homeland Security to certify all refugees from Syria and Iraq don't present a security threat. He argued that after a recent bipartisan House vote on the issue included significant Democratic support, the requirement needed to be in the budget deal, even though Senate Democrats had vowed to block it.
And he complained that Senate Majority Leader Mitch McConnell, a fellow Republican, may get a campaign finance provision inserted in the bill that critics say would increase the influence of wealthy donors to political parties.
"Forty-seven Democrats said they were for it, the chairman of the Homeland Security Committee says ISIS is exploiting it, and we're not going to put it on the omnibus, but we may put in a special provision to help campaign finance for the political parties?" Jordan said Thursday. "Do you think the American people are going to like that? Of course it has to go on the bill."
But as one side pushes for its priority, the other wants something in return, so aides and members close to the process break out the adage "nothing is agreed to until everything is agreed to."
"There are a lot of movable parts here. It's a chess board. Everyone is thinking about what might be their next move," said Sen. Ron Wyden of Oregon, the top Democrat on the Finance Committee, which is negotiating the tax package.
Republican Sen. Roy Blunt, R-Missouri, acknowledged that while the negotiations are tough, the atmosphere in the Capitol is not as intense as in past years.
"I don't know that everybody is that relaxed, but I think most people have determined that there is not much they can do about these final negotiations," he said. "This is going to be decided by three or four people, and most of us are not one of those three or four people."