WASHINGTON — Senate Republicans blocked a move by Democrats today to add more than $40 billion in checks for the elderly, disabled veterans, and the unemployed to a bill to stimulate the economy.

The 58-41 vote fell just short of the 60 required to break a Republican filibuster and bring the Senate version of the stimulus bill closer to a final vote. The Senate measure was backed by Democrats and a handful of Republicans but was strongly opposed by Republican leaders and President Bush, who objected to the costly add-ons.

The vote left the $205 billion Senate stimulus bill in limbo and capped days of partisan infighting and procedural jockeying over the measure. Senators Clinton and Obama flew to Washington for the vote. A Republican presidential front-runner, Senator McCain of Arizona, did not vote.

Supporters actually had 59 votes in favor of the Democratic proposal, but the majority leader, Senator Reid of Nevada, switched his vote to ‘no’ at the last moment, a parliamentary move that allows him to bring the measure up for revote.

Republican leaders objected to add-ons such as a $14.5 billion unemployment extension for those whose benefits have run out, $1 billion in heating aid for the poor, and tax breaks for renewable energy producers and coal companies.

The measure builds upon a less costly $161 billion House-passed bill providing checks of between $600 and $1,200 to most taxpayers and tax breaks to businesses investing in new plants and equipment.

The Senate version would provide checks of between $500 and $1,000 to a broader group that includes 20 million older Americans, 250,000 disabled veterans and taxpayers making up to $150,000 for singles — or $300,000 for couples.

Mr. Reid denied Republicans an opportunity to offer changes to the measure, provoking the filibuster. The calculus was that enough Republicans would relent in the face of political pressure to vote for unemployment insurance and heating aid to join with Democrats to force the measure through.

“Our constituents will look at us as the folks that slowed it down, (and) added a bunch of spending to it,” Senator Kyl of Arizona, the Republican whip, said. He called the measure “a Christmas tree package.”

The Republican leader, Senator McConnell, Republican of Kentucky, said he wants to amend the measure to add the provisions favoring disabled veterans and the elderly and making clear that illegal immigrants can’t get rebate checks.

Mr. Reid rejected the offer — at least for the time being — but Republicans seemed confident he would eventually agree to comparable changes since the alternative would be to approve the House bill and leave retirees living on Social Security and disabled veterans without rebate checks.

The dramatic vote came after an intense lobbying effort by Democrats to convert wavering Republicans, including several facing tough re-election fights. Their efforts were getting a boost from outside groups leaning on senators to back the package, including home builders, manufacturers, and the powerful seniors lobby.

Republican leaders, working to stem defections, were assuring Republicans that they would have another chance to support adding senior citizens and disabled veterans to the aid plan even if they opposed the Democrats’ bill.

That wasn’t enough for Senator Domenici, Republican of New Mexico, who threw his support behind the measure during a brief floor debate.

“I made my decision on what was best for New Mexico and what’s best for America,” he said.

But other targets, such as Senator Sununu, Republican of New Hampshire, stuck with Mr. McConnell.

Asked yesterday whether the administration would accept adding rebates for the elderly and disabled veterans to the stimulus measure, Treasury Secretary Paulson declined to say definitively, but he told the Finance Committee, “I’m sure we’ll be able to work something out and get something quickly done that’s broad-based.”

The dispute has slowed down the stimulus measure, but there’s no indication that it will delay rebate checks, which are expected to begin arriving in May. The rebates will be based on 2007 tax returns, which aren’t due until April 15.