WASHINGTON — With the clock ticking toward a possible government shutdown, spending-cut talks between Senate Democrats and the Republicans controlling the House have broken off in a whom-do-you-trust battle over legislation to keep operations running for another six months.

Democrats have readied a proposal to cut $20 billion more from this year’s budget, a party official said, but they haven’t yet sent it to House Republicans. They say it’s unclear whether the majority Republicans would accept a split-the-difference bargain they’d earlier hinted at or will yield to demands of tea party-backed GOP freshmen for a tougher measure.

The official spoke on condition of anonymity to discuss internal deliberations.

“Republicans refuse to negotiate,” Senate Majority Leader Harry Reid declared Monday. “The infighting between the tea party and the rest of the Republican Party — including the Republican leadership in Congress — is keeping our negotiating partner from the negotiating table. And it’s pretty hard to negotiate without someone else on the other side of the table.”

Republicans countered that it’s the Democrats who have yet to offer a serious plan to wrestle spending under control and that a Democratic offer from last week to cut $11 billion from the budget was laced with gimmickry.

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 vehicle for the latest fighting is 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. Other major tests will soon follow, as House Republicans unveil a blueprint to attack the broader budget mess next week — and a must-do measure to maintain the government’s ability to borrow money to meet its responsibilities. Within that context, the current battle involves relatively modest amounts.