Federal spending negotiations that just last week seemed headed in the direction of a hard-fought agreement between House Republicans and Senate Democrats have stumbled yet apart again, as Republican leadership in the House on Monday night prepared yet another short-term measure to avoid a looming government shutdown.

The latest stopgap measure is described as "more aggressive" than past measures, as it will seek $12 billion in cuts while approving spending for just one more week. And it will propose securing Pentagon funding for the rest of the fiscal year, which would take a major component of federal spending off the table.

Such a measure would be remarkable, were it to pass the GOP-controlled House, given that some of the party's most conservative members have vowed to vote against any more stop-gap measures. But even if the House passes the plan before the current spending measure expires after Friday, it is unclear whether Democrats who control the Senate will get on board.

The maneuverings in Congress serve as a prelude to a White House summit planned Tuesday.

The White House said the president has invited House Speaker John Boehner, Senate Majority Leader Harry Reid and top negotiators on the appropriations committees to a session.

President Obama's spokesman Jay Carney said time was running short and the president would urge the lawmakers to reach an agreement.

Carney said the White House was optimistic that a shutdown could be averted, but Boehner, R-Ohio, said there were still disagreements about how much to cut spending through Sept. 30, the end of the budget year. He accused the White House of bringing too many phony budget cuts to the table in hopes of restoring reductions made by Republicans in February.

"Despite attempts by Democrats to lock in a number among themselves, I've made clear that their $33 billion is not enough and many of the cuts that the White House and Senate Democrats are talking about are full of smoke and mirrors," Boehner said in a statement. "That's unacceptable."

Democratic officials knowledgeable about the proposals said the administration's ideas including taking unused money from federal highway programs and leftover funds from a program providing health care to middle-class families. Both ideas count in congressional budget terms as savings that could be used to pay for spending elsewhere in the day-to-day budgets of domestic agencies, but their practical effect is nil.

The officials spoke on condition of anonymity to discuss proposals that haven't been made public.

Despite his protests, Boehner's own Republican appropriators have claimed $5 billion in questionable savings from capping payments from a trust fund for crime victims.

At issue is long-overdue legislation required to fund the operating budgets of every Cabinet agency for the ongoing budget year, which is already half over.

Negotiations have centered on cuts in the range of $33 billion -- a figure that has allowed congressional staff aides to works through the measure line by line -- but Boehner has repeatedly said there is no agreement on how much to cut. The White and Democrats also are balking over more than 50 policy provisions that House Republicans have attached to the measure.

Such policy "riders" include cutting off implementation of the new health care law and forbidding taxpayer money from going to Planned Parenthood.

Fox News' Chad Pergram and the Associated Press contributed to this report.