Senate Finance Chairman Max Baucus (D-Mont.) is on the brink of garnering a filibuster-proof majority for his measure designed to lower Medicare drug prices, even as one of the original sponsors of the bill threatens to unravel a delicate bipartisan coalition.

Baucus’ rewrite of the legislation — which is slated to be taken up in committee today, with Senate floor consideration as early as next week — appears likely to pick up former Republican and Democratic opponents. Rather than forcing Medicare officials to negotiate with drug companies for lower prices, as earlier versions of the bill did, Baucus crafted a measure that simply would allow the practice without mandating it.

That change, along with Democratic gains in November, has put Baucus awfully close to getting the 60 votes necessary to beat back an inevitable filibuster attempt by Finance ranking member Chuck Grassley (R-Iowa).

“We’re right on the cusp of 60 votes, in my view,” said Sen. Ron Wyden (D-Ore.), a leading sponsor of the earlier versions. He added, “I think I have a pretty good idea of which Republicans are reachable, and I’ve talked to most who voted with me” in 2006, when eight current Republican Senators supported an amendment advocating for Medicare negotiating authority.

Wyden signed off on Baucus’ changes because he said the existing ban on Medicare officials negotiating with drug companies for lower costs should be lifted. And he said he would be first among many in pressing the Health and Human Services Department, which oversees Medicare, to use the authority once they have it.

“Medicare should not be the only organization on the planet outlawed from negotiating,” he said.

But Sen. Olympia Snowe (R-Maine), who has been a longtime co-sponsor of the earlier versions with Wyden, greeted the changes to Baucus’ bill with “open-armed surprise about why after years of tough talk by the Democrats they are taking a sedative” on this bill, said Snowe spokesman David Snepp.

Snepp added that Snowe believes the bill has been significantly weakened and that she does not want the decision on whether to negotiate lower prices to be left up to the discretion of whichever presidential administration happens to be in power. Besides hinting at vetoing the bill, the Bush administration would be highly unlikely to use the power, for example.

Snepp would not reveal whether Snowe would offer amendments in committee, on the floor or not at all.

And even though Snowe is expected to support the Baucus bill on final passage, Democrats said they still see her as a threat, particularly during today’s markup.

Besides negotiating with fence-sitting Republicans such as Sen. Gordon Smith (Ore.), Baucus also had to convince Democrats on the committee to vote against any Snowe amendment to replace his bill with language to require the Health and Human Services secretary to broker lower drug prices, said one Senate Democratic aide.

The aide said the argument to Democrats was that “this vehicle gives us the best chance” at passage, adding, “People will be surprised who will like this bill.”

Last year, Democrats garnered 54 votes for mandated prescription drug negotiation authority, though the vote was nonbinding as part of the fiscal 2007 budget resolution. If Democrats hold that support — which would now include the votes of the nine newly elected Senate Democrats and the eight Republicans who supported it last year — they would have 58 votes. (The tally does not include Democratic South Dakota Sen. Tim Johnson, who has been recuperating from a stroke last December, but he likely would support the bill.)

So picking up more Republicans is crucial, but increasingly possible. Sen. Norm Coleman (R-Minn.), who previously has expressed a reluctance to support the bill, said Tuesday that he was open to the bill because “apparently there’s very benign language coming out of the Senate.” Still, he cautioned that he is concerned that any conference between the Senate measure and the House bill, which does require the HHS secretary to use the negotiating power, would result in a bill he could not support.

“I just want to make sure it’s good policy and not political gamesmanship,” Coleman said of his wariness that the changes Baucus made were merely to get the bill to conference to strengthen it.

Other targets of the bill’s changes were Sens. Ben Nelson (D-Neb.) and Trent Lott (R-Miss.), who opposed the amendment last year, as well as Sen. Lindsey Graham (R-S.C.), who voted for the proposal, said one source with knowledge of the negotiations. It was unclear whether any of those Senators would vote for the new bill.

But Grassley said he was not swayed by the changes to the measure. “I have to fight it,” he said, explaining that the current system of private prescription providers negotiating with drug companies is working quite well. “If it ain’t broke, don’t fix it.”

And one Republican who voted with Democrats previously said she still was undecided about supporting the new bill on the floor.

“I don’t know,” said Sen. Lisa Murkowski (R-Alaska).

One senior Senate Democratic aide said Republican leaders are unlikely to give their members a free pass on the bill next week. The aide said it would be hard to believe that Senate Minority Leader Mitch McConnell (R-Ky.) would not lean on some of his Senators to prevent Democrats from breaking the filibuster.

“They’ll free who they need to and keep others,” predicted the aide.

In fact, Republicans are largely relying on reports by the nonpartisan Congressional Budget Office, stating that negotiation authority would not significantly lower the costs of the program. The most recent missive from the CBO came this week, reiterating the agency’s belief that giving drug price negotiating authority to Medicare would have “a negligible effect” on the cost of the program to taxpayers.

“It throws a big wet blanket on their Medicare plans,” said one Senate GOP leadership aide.

The April 10 CBO letter, requested by Baucus’ staff, states, “Without the authority to establish a formulary or other tools to reduce drug prices, we believe that the [HHS] Secretary would not obtain significant discounts from drug manufacturers across a broad range of drugs.”