The specter of a partial government shutdown looms again as Congress returns to Washington with Democrats and Republicans as far apart on spending priorities as they were when winter turned to spring.

The best the two parties have been able to agree on so far this year has been stopgap spending measures to avoid any disruptions in government services while they tried to work out sharp differences over national spending priorities.

The vehicle for the debate, left simmering when lawmakers went back to their districts last week, is must-do legislation to bankroll the day-to-day operating budgets of federal agencies _ including military operations in Iraq and Afghanistan _ through the Sept. 30 end of the budget year.

Last month, House Republicans passed a measure cutting more than $60 billion from the $1.1 trillion budgeted for such programs last year. All the savings were taken from domestic programs and foreign aid, which make up about half of the pot. Democrats in the Senate killed the measure as too extreme, citing cuts to education, health research, food inspection and other programs and services.

The shutdown scenario was mostly set up in last year's midterm election campaign, when Republicans emphasized sharp spending cuts to attack mounting federal deficits and won control of the House, enough additional political clout to more strongly challenge President Barack Obama on budget issues.

The GOP promised that it would ratchet spending down to 2008 levels and force Obama to backtrack on generous budget increases made on his watch. To meet the promise, GOP leaders initially pressed for about $35 billion in cuts in a proposal that took account of the fact that the budget year was almost halfway over.

That idea didn't sell with tea party activists, and House Speaker John Boehner was forced to almost double the size of the cuts, driving away any potential Democratic support. But that meant the halfway point between the House-passed measure and a proposal advanced by Democrats controlling the Senate was roughly where Boehner started out in the first place.

"The speaker knows that when it comes to avoiding a shutdown, his problem is with the tea party, not Democrats," said Sen. Chuck Schumer, D-N.Y.

Time is running short. Staff-level negotiations last week ran aground, and the principals are going to have to pick up the pace to have any chance of making an April 8 deadline to avoid a partial shutdown of the government. Right now it appears that the shutdown that both sides have sworn to avoid is possible _ if not probable.

The frustration boiled over on Friday, with Republicans criticizing Democrats for not presenting significant cuts. An offer a few days earlier had ponied up just another $10 billion or so, GOP officials said, which prompted House Majority Leader Eric Cantor to accuse Democrats of "negotiating off of the status quo and refusing to offer any sort of serious plan for how to cut spending."

The tough rhetoric was matched by volleys from Boehner, R-Ohio, and other House GOP leaders. That prompted Schumer to accuse Republicans of blowing up a near agreement on a "top line" of spending cuts that would have likely given Republicans more than half of their $60 billion-plus in reductions.

"After days of positive negotiations, with significant flexibility shown by the speaker, the House Republican leadership is back to agonizing over whether to give in to right-wing demands that they abandon any compromise on their extreme cuts," he said.

Democrats also say that House Republicans insist on using House-passed legislation slashing more than $60 billion from the current-year budget as the starting point for talks, pulling back from an agreement with Boehner's office to work off a baseline essentially set at last year's levels.

Boehner appears to be in a no-win situation. Any agreement with Obama is sure to incite a revolt among hard-line tea party figures who want the full roster of cuts and an end to funding for Obama's signature health care law. And social conservatives are adamant that the measure cut off money for Planned Parenthood clinics that provide abortions in addition to the family planning services the government funds. Any attempts to outmuscle Obama with legislation that pleases tea partiers, however, would surely incite a shutdown.