The fate of $600-$1,200 rebate checks for more than 100 million Americans is in limbo after Senate Republicans blocked a bid by Democrats to add $44 billion in help for the elderly, disabled veterans, the unemployed and businesses to the House-passed economic aid package.

GOP senators banded together Wednesday to thwart the $205 billion plan, leaving Democrats with a difficult choice either to quickly accept a House bill they have said is inadequate or risk being blamed for delaying a measure designed as a swift shot in the arm for the lagging economy.

The tally was 58-41 to end debate on the Senate measure, just short of the 60 votes Democrats would have needed to scale procedural hurdles and move the bill to a final vote. In a suspenseful showdown vote that capped days of partisan infighting and procedural jockeying, eight Republicans — four of them up for re-election this year — joined Democrats to back the plan, bucking GOP leaders and President Bush, who objected to the costly add-ons.

Democrats choreographed the vote for maximum political advantage, presenting their aid proposal as a take-it-or-leave-it proposition for Republicans and calling back their presidential candidates to make a show of party unity behind their stimulus plan. They calculated that Republicans would pay a steep price for opposing rebates for older Americans and disabled veterans, as well as heating aid for the poor, unemployment benefits and a much larger collection of business tax breaks than the House approved.

Even after their effort fell short Wednesday, Democrats seemed determined to keep the pressure on Republicans to accept the measure, threatening to hold more votes on it in the coming days.

Majority Leader Harry Reid, D-Nev., is "going to give Republicans a chance to reconsider their vote against efforts to strengthen the economy by helping those who need it most," his spokesman, Jim Manley, said Wednesday night.

Republicans said they were ready to accept rebates for seniors and disabled veterans and accused Democrats of delaying the stimulus plan for political gain and loading it down with special-interest extras.

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

The White House, which has carefully avoided issuing threats about the package despite Bush's opposition to the add-ons, urged the Senate to move fast to approve a stimulus plan.

"To be effective, this economic growth package must be timely, so it is crucial that the Senate now move quickly to pass a bill that will deliver relief to our economy," press secretary Dana Perino said in a statement after the vote.

Democratic presidential candidates Hillary Clinton of New York and Barack Obama of Illinois flew to Washington for the vote. GOP front-runner John McCain of Arizona did not vote.

Supporters actually had 59 votes in favor of the Democratic proposal, but Reid switched his vote to 'no' at the last moment, a parliamentary move that allows him to bring the measure up for a 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 $161 billion House-passed bill providing $600-$1,200 checks to most taxpayers and tax breaks to businesses investing in new plants and equipment.

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

It would extend unemployment benefits for an additional 13 weeks for those whose benefits have run out, with 13 more weeks available in states with the highest jobless rates. The bill also includes $10 billion in tax-free mortgage revenue bonds to help homeowners refinance subprime loans.

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 support unemployment insurance and heating aid to join Democrats and force the measure through.

GOP leader Mitch McConnell, R-Ky., said he wants to amend the measure to add rebates for disabled veterans and their widows and the elderly, and language — also included in the Democrats' package — making clear that illegal immigrants can't get rebate checks.

"We didn't block the proposal," McConnell said. "We just said there's a better way to go and there's an alternative."

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.

House Speaker Nancy Pelosi, D-Calif., who backs a stimulus bill with Treasury Secretary Henry Paulson and Minority John Boehner, R-Ohio, said House lawmakers are "very receptive to additions to our bill which ensure that disabled veterans and additional seniors are eligible" for rebate checks and want to make sure illegal immigrants are denied them.

A Pelosi spokesman said her statement did not represent a break with Reid, even though she seemed to praise McConnell's approach and was silent on Democratic add-ons such the provision benefiting coal companies. Pelosi prefers to try to extend unemployment benefits in a later bill.

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

Republicans were under enormous pressure from their own leaders not to support the Democrats' plan. Working to stem defections, GOP leaders assured their rank and file 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 Sen. Pete Domenici, R-N.M. who threw his support behind the measure.

"I'm hopeful that I have chosen the right path," he said just before the vote. "I made my decision on what was best for New Mexico and what's best for America."