The current bill funding the federal government expires Thursday night. (Karen Bleier/AFP/Getty Images)

Plans to quickly approve a $1.1 trillion spending package to keep most of the federal government open through the end of the fiscal year fell apart late Monday, increasing the chance lawmakers will miss a Thursday deadline.

Just in case, top appropriators said Monday that they were ready to pass a short-term extension of a few days in order to give the House and Senate more time to pass the final bill and end the least productive congressional session in modern history.

Top leaders spent most of Monday reviewing the final details of the massive spending bill, but hopes of unveiling the legislation by midnight were dashed amid last-minute disagreements over the renewal of a terrorism insurance program.

For months, Sen. Charles E. Schumer (N.Y.), a lead Democratic broker, and Rep. Jeb Hensarling (R-Tex.), chairman of the House Financial Services Committee, led talks to reauthorize the Terrorism Risk Insurance Act, which provides for a government-backed program to protect against catastrophic terrorist attacks. Both sides had reached agreement on continuing the program by Monday evening, but differences remained regarding proposed changes to 2010 financial regulatory reforms that were sought as part of the deal, according to aides familiar with the impasse.

Leaders still hope to release the bill Tuesday, giving Congress less than 48 hours to beat the deadline. While the GOP-controlled House would be able to move quickly to pass the bill, Democrats in charge of the Senate would need to secure an agreement from Republicans to skip procedural rules and pass the bill by Thursday night. It was unclear late Monday whether GOP leaders would be able to get such an agreement from Republican senators hoping to strip federal agencies of the money and power to enforce President Obama’s recent executive action changing the nation’s immigration laws.

A $1 trillion spending bill unveiled Tuesday keeps most of the federal government funded through September. Here, The Post's Ed O'Keefe points out a few of the most notable components of the legislation. (Davin Coburn/The Washington Post)

Any delay in releasing the bill means that “it can’t be pretty — it never is,” said Sen. Jeff Sessions (R-Ala.). Sessions is among the Republicans hoping to use the spending bill to punish Obama for using his executive authority. But Monday night he conceded that he probably wouldn’t prevail — and said he was “torn” over whether to slow or block the spending bill in response.

“You’re concerned about what the president did and want to respond — but you don’t want to be slowing things down to the point that a near-shutdown occurs,” Sessions said, adding later that failing to stop Obama’s executive orders would be “an abdication of congressional responsibility.”

The legislation would provide full funding for 11 of the 12 appropriations bills Congress is supposed to pass each year, but it would extend funding for the Department of Homeland Security, which has jurisdiction over immigration enforcement, only through early next year. The shorter deadline for DHS would allow Republicans to craft a legislative response to Obama’s immigration orders next year instead of now.

The deal would be consistent with spending caps agreed to by the White House and lawmakers last year. Senior aides said the deal is expected to include roughly $5 billion of the $6.2 billion Obama requested to fight Ebola.

Several congressional Democrats said their support for the legislation was dependent on whether Republicans try tucking any policy “riders” into the bill. Eleanor Holmes Norton, the District of Columbia’s nonvoting Democratic representative, said she was waiting to see about a GOP proposal to block District leaders from implementing plans to legalize marijuana possession, which city voters approved last month.

“It’s hard to know” what Republicans might do, she said, “because we haven’t gotten started yet. They’re trying to stop us before we leave the home plate.”

Speaker John A. Boehner (R-Ohio) has vowed to adjourn the House by Thursday and has predicted that the spending bill will pass with bipartisan support. Leaders of the House and Senate appropriations panels worked over the weekend on the bill while GOP leaders carefully built support, paying special attention to the potential for conservative fury.

House Minority Leader Nancy Pelosi (D-Calif.) won’t say whether she’ll encourage colleagues to vote for or against the legislation until she sees the final text, aides said.

Passing the spending bill is just one of several pieces of unfinished business expected to dominate the week. On Tuesday, the Senate Intelligence Committee is set to release a long-awaited report on the CIA’s interrogation tactics. Jonathan Gruber, the former Obama administration consultant who earned the ire of Republicans for his comments on voters’ perceptions of the Affordable Care Act, is slated to appear before a House panel Tuesday. Secretary of State John F. Kerry is scheduled to testify on continuing U.S. military operations against the Islamic State.

And Democrats are expected to use their fleeting days of Senate control to confirm more of Obama’s nominees to government posts. The president’s picks for several senior State Department positions and for surgeon general are awaiting consideration, and Majority Leader Harry M. Reid (D-Nev.) hasn’t ruled out keeping the Senate open beyond this week to hold votes.

As they prepare to take control of the Senate, Republicans also are expected to decide Tuesday whether to restore the old filibuster rules. Democrats took the dramatic step last year of eliminating filibusters for most presidential nominations, a move they said was needed to fix a broken system. Minority Leader Mitch McConnell (R-Ky.) called the change a “power grab” and vowed to restore the old rules, but has since backed away from that statement.

Other GOP senators who once railed against changing the rules said they might now support keeping them. “I’ve kind of gradually come to the conclusion: Keep the rule the way it is. Frankly, even with the old rule, the vast majority of presidential nominees went through,” Sen. Orrin G. Hatch (Utah), the longest-serving GOP senator, said last week.