WASHINGTON — Legislation to extend unemployment subsidies for hundreds of thousands of Americans who have exhausted their jobless benefits teetered on the edge of collapse on Thursday, as Senate Democrats and Republicans traded bitter accusations about who was to blame for an eight-week impasse.

Senate Republicans and a lone Democrat, Ben Nelson of Nebraska, joined forces to filibuster the bill in a procedural vote on Thursday. Visibly frustrated, the majority leader, Harry Reid, Democrat of Nevada, said he would move on to other business next week because he saw little chance of winning over any Republican votes.

The vote was 57 to 41, with the Democrats falling three short of the 60 votes needed to advance the measure.

“You’ll hear a lot of excuses,” Mr. Reid said at a news conference. “The bottom line is the minority just said no.”

Responding to Republican demands, Mr. Reid on Wednesday night introduced yet another version of the legislation, which also includes important tax changes. But even as he unveiled the new package, aides conceded he did not have the votes.

The Senate Republican leader, Mitch McConnell of Kentucky, has insisted that the bill not add to the deficit. Democrats argued that they had found ways to cover the entire cost of the $112 billion measure, with the exception of the $35.5 billion extension of unemployment benefits, which some Republicans said they could accept.

But some Republicans who had been negotiating with Mr. Reid said they remained opposed to tax increases in the bill, and Mr. McConnell insisted that Republicans would not support any increase in the deficit.

To dramatize the point, after blocking the Democrats’ bill, Mr. McConnell proposed a one-month extension of unemployment benefits and some other safety-net spending, to be paid for with about $10 billion in unspent money from last year’s economic stimulus program.

Democrats had already proposed using some stimulus money to help pay for the bill, and Mr. McConnell said he was simply endorsing the same idea.

“The only thing Republicans have opposed in this debate are job-killing taxes and adding to the national debt,” Mr. McConnell said. Anticipating that Democrats would reject his proposal, he added, “Their commitment to deficit spending trumps their desire to help the unemployed.”

Senator Max Baucus, Democrat of Montana and chairman of the Finance Committee, who is the primary sponsor of the legislation, said the bill had been cut back by about $100 billion in response to Republicans’ demands for a smaller package.

In the latest version, the Democrats pared a provision to extend higher Medicaid reimbursement for the states, to $16 billion from $24 billion, and also found offsets in spending to cover the cost.

Democrats, citing data by the National Employment Law Project, say that without Congressional action, 1.2 million Americans will exhaust their jobless benefits by the end of the month.

The legislation would reinstate numerous expired tax breaks, as well as provided an array of safety-net spending. To help cover the cost, Democrats also proposed shifting some unspent money from last year’s economic stimulus program, a move that prompted Republican cheers.

Even some Democrats have expressed deep reservations about adding to the nation’s fast-growing deficit. Mr. Nelson and Senator Joseph I. Lieberman, independent of Connecticut, who caucuses with the Democrats, have joined with Republicans in opposing the bill.

And House Democrats did not include the extra Medicaid money for states in its version of the legislation out of concern for the cost. Senate Democrats restored the money at the urging of governors and state legislatures.

At a news conference Thursday before the Senate vote, Democratic leaders voiced exasperation at the stalled legislation, and Mr. Reid said that if the vote failed, he would move on to other legislation, beginning with a bill intended to help small businesses create jobs.

“We’re where we are because Republicans have said no to helping America,” Mr. Reid said.