Democrats and Republicans traded heated barbs Tuesday over Senate Majority Leader Harry Reid’s (D-Nev.) plan to push through a $245 billion extension of Medicare physician payments, accusing each other of trying to use the popular program for political gain.

The fighting left the future of the “doc fix— in doubt, particularly as an increasing number of Democrats started to line up against it and top Democrats conceded they do not have the votes to block a bipartisan filibuster.

Still, Democratic Senate leaders tried to blame the GOP for tripping up the measure.

“Republicans believe that they can derail health care reform by defeating the doc fix,— Majority Whip Dick Durbin (D-Ill.) said. “That’s what this is all about. Another way to slow down the process and stop health care reform.—

Meanwhile, a two-year, $25 billion alternative being negotiated by Budget Chairman Kent Conrad (D-N.D.) and Finance ranking member Chuck Grassley (R-Iowa) appeared to be gaining steam. That measure would offset the costs of the doctors’ payments extension over that period, meeting the concerns of a handful of Democrats who want the bill paid for. Aides said as many as eight Democratic Senators have said they would not vote to end a filibuster of the doc fix in its current form.

“I’m not going to advance things that aren’t paid for by cloture vote or any other vote,— Conrad said. “I’ve had many public and private conversations. My message is as consistent and clear as it can be: We have got to pay for things.—

Several Democratic Senators noted that the doc fix bill was discussed during the weekly Conference lunch and that a number of alternatives to it were floated. Democrats indicated that there is increasing interest in the Conrad-Grassley plan or another short-term Medicare payment extension that would also include offsets.

Senate Republicans accused Democrats of using the Medicare payment measure as a way to “buy— support from doctors’ groups for their broader health care reform bill, which is being finalized by Reid, the White House and Finance Chairman Max Baucus (D-Mont.) and Sen. Chris Dodd (D-Conn.).

The Hill newspaper reported Monday that Reid had hoped to strike a deal with the doctors organizations: Democrats would advance the doc fix in exchange for the groups’ support on the larger health care overhaul.

“Sen. Reid and others are meeting with physicians in order to buy their support. We all know that the selling of one’s body is one of the oldest professions in the world. And the [American Medical Association] is engaged in basically selling the support of its body by leveraging, by throwing future generations under the bus, by in essence urging that we as Congress pass this week a quarter-of-a-trillion-dollar spending bill, unpaid for,— Sen. Bob Corker (R-Tenn.) said during a fiery floor speech Tuesday.

Given the level — and intensity — of bipartisan opposition to Medicare measure, it was unclear Tuesday afternoon how Reid would decide to proceed.

Reid had initially hoped to begin debate on the bill Monday but scrapped a planned vote to begin debate when it became clear that he did not have enough support.

Reid finds himself in a difficult position, as he had hoped to use the 10-year doctors’ payment extension as a way to sweeten the overall health care reform effort for the AMA and other doctors groups. Democrats acknowledged Tuesday that they would now need GOP votes to move ahead on the bill.

“We need Republican support. If the Republicans support strengthening Medicare, saving it so that doctors don’t leave Medicare, they need to show it with their votes. … We don’t have 60 votes on our side of the aisle,— Durbin said, adding that at this point leadership is weighing various alternatives.

“How you pay for them and how many votes you put on the board is what it’s about— for Democratic leadership at this point, Durbin said.