If it weren’t clear already that lawmakers — especially Republicans — want to avoid another government shutdown, the overwhelming optimism Monday that Congress will pass an omnibus spending measure for the first time in two years tips their hand.

Democratic and Republican aides in both chambers believe that Senate Appropriations Chairwoman Barbara A. Mikulski, D-Md., and House Appropriations Chairman Harold Rogers, R-Ky., will come to an agreement this week on a more than $1 trillion bill to fund the government. But even with the highest hopes for swift passage, negotiating a behemoth spending package that touches every corner of the government is not easy.

Mikulski told CQ Roll Call that four of the 12 appropriations bills have been completed — the Legislative Branch, Commerce-Justice-Science, Military Construction-VA and Transportation-HUD, while the three most challenging bills are Defense, Labor-HHS-Education and Interior-Environment.

The Affordable Care Act and abortion remain sticking points, Mikulski said. “If something begins with an ‘A’ it’s a sticking point, and I’m trying to get to the ‘Zs’,” she said.

The goal is to announce a deal by Wednesday and file the bill by Friday. Senate Democratic aides said the House would ideally file the legislation by the end of this week and get it on the Senate floor next week, ahead of Congress’ Jan. 15 deadline to avert a shutdown.

One aide said that the “overwhelming majority of issues” were resolved over the break and noted there has been “minimal conflict” over the controversial policy riders that usually bog down such negotiations.

Although there certainly is consternation among Republicans over funding the president’s health care law, sources say even some of the staunchest conservatives acknowledge that shutting down the government in October over the measure was a failure. And with the eleventh-hour injunction from the Supreme Court on the law’s contested contraception mandate and other lawsuits emerging, Republicans believe they have found more appropriate channels for their frustration.

“Every member who voted for the budget agreement likely would vote for this,” said one House GOP leadership aide of the 169 Republicans who voted in December to give appropriators their top-line numbers for the next two fiscal years. House Republican leadership aides approached for this story asserted that they were confident the omnibus spending bill would pass.

Of course, leaders will still have to round up the votes, once the massive bill is revealed to the public — especially given that it is certain to include heartburn-inducing items for the GOP rank and file and fodder for outside groups to attack.

On Sunday, Senate Majority Leader Harry Reid, D-Nev., told CBS’ “Face the Nation” that even as he was encouraged by the deal between budget chiefs Patty Murray, D-Wash., and Paul D. Ryan, R-Wis., he was fearful that GOP lawmakers might renege on their earlier commitment and close down the government.

“I am afraid. Why am I afraid? It was just matter of couple of months ago that two-thirds of the Republicans in the House of Representatives voted to keep the government closed and default on the debt,” Reid said. “So I hope we can get this done, but … I am really concerned about what’s going on with Republicans in Congress. Repeat to your viewers. Two-thirds of the people in the House of Representatives are Republicans who voted to close the government, keep it closed more than 16 days and default on our debt. I mean, I want this to pass. I hope it does. It should, that we have an omnibus appropriations bill. But I don’t know.”

The success or failure of the package will test whether a Congress that has bridged differences over spending levels can govern, turning a page from 2013’s abysmal record on that front.

The Senate notably failed to approve any appropriations bills in 2013, as Republicans one by one rebuffed their colleague Susan Collins of Maine in a dramatic and awkward vote to filibuster the Transportation-HUD spending legislation.

Despite that, all eyes will likely be on the House anyway. In the lead-up to the December budget agreement, Rogers insisted that with higher-than-sequestration top-line numbers — which he then received from Murray and Ryan — he would be able to shepherd all 12 spending bills through the chamber by Jan. 15.

The proclamation at the time seemed ambitious at best, yet Rogers’ ahead-of-the-curve optimism is turning into reality, according to House Appropriations aides.

“Good progress is being made,” a Republican appropriations aide said. “Staff and members talked continually over the break. The goal remains to negotiate and complete all 12 funding bills before the January deadline.”

“Staff and members … were working throughout the holiday break and over the weekend,” a Democratic appropriations staffer echoed, adding that ranking member Nita M. Lowey, D-N.Y., “has been very much involved” in discussions.

“There are still open issues that need to be resolved related to both dollar figures and policy, but we are making steady and significant progress and are cautiously optimistic about meeting the January deadline,” the Democratic aide continued.

Emma Dumain, Niels Lesniewski and Tamar Hallerman contributed to this report.