Senate Republican leaders are trying to determine whether they have enough support in the their Conference to help Sen. Tom Coburn (R-Okla.) filibuster a public lands bill that already cleared the chamber once this year.

“There’s a significant portion of the Conference that’s open to the idea,— one senior Senate GOP aide said.

A test vote is scheduled for tonight, and 60 votes are needed to bring the measure up for consideration.

If Republicans decide to try to block the public lands bill, it would represent a dramatic reversal from earlier this year, when 17 GOP Senators supported moving it through. At that earlier vote, those Senate Republicans rebuffed Coburn’s pleas to try to amend the package and win a fight that he waged with Majority Leader Harry Reid (D-Nev.) for the better part of the 110th Congress.

The public lands package, which on its face enjoys strong bipartisan support, was the first measure to come before the Senate this year, and the vote to beat back Coburn’s filibuster was seen as the first major victory for Reid. The win was sweet, not only because Reid had finally overcome Coburn’s objections, but also because it signaled that he may be able to stop repeated GOP filibusters of his legislative agenda.

The ostensible purpose of the GOP filibuster strategy last year was to protect the party’s ability to offer amendments to legislation — an argument that was rejected by nearly half of all GOP Senators in that January public lands bill vote. But recently the Senate GOP has re-embraced the “minority rights— argument — they unified just last week to force more amendment votes on a $410 billion omnibus spending bill.

The lands package has been nicknamed the “Tomnibus— because it is a catch-all bill of public lands measures that Coburn blocked in the last Congress. Coburn was also successful in the 110th at persuading his Republican colleagues to stand with him, but that was when the Senate had a more robust 49-Member minority.

GOP aides noted that this time, the entire Conference would have to be unified behind Coburn. It was unclear late last week whether all 41 GOP Senators — the bare minimum needed to filibuster — were on board with the plan. Coburn made his plea for unity at the Senate Republican Steering Committee lunch Wednesday, the senior Senate GOP aide said.

The aide said Senate GOP leaders could decide to allow the bill to come up for debate but block it before it can pass. However, no decisions have been made as the leadership continues to survey Members about whether there is a will to filibuster.

Either way, Coburn plans to use all the procedural tactics at his disposal to force an extended debate on the bill, his spokesman John Hart said.

“If Dr. Coburn receives anything less than a full and open debate on this, he will do everything in his power to force the Senate to spend the maximum amount of time on this bill,— Hart said.

Coburn has a number of amendments, Hart said, adding that if Coburn is given a chance to offer them, he would not try to block the bill. Reid has indicated that he won’t allow amendments to the measure and is prepared to jump through whatever procedural hoops necessary to get the bill passed a second time.

Though the Senate already passed the measure, it failed to garner the two-thirds support of House Members to clear it on suspension last week.

House Republicans are balking over provisions in the measure setting aside lands that might otherwise be used for energy exploration. Some GOP Members, including Coburn, also oppose authorizing pet projects such as a $3.5 million plan to help the city of St. Augustine, Fla., celebrate its the 450th birthday six years from now.

Now that House Republicans successfully blocked the bill, Coburn hopes the Senate retread will give him more momentum with his colleagues.

“Sen. Reid has spent months describing this bill as noncontroversial, but 144 Members of the House have a different view,— Hart said.

Reid is bringing the bill back up only because of House GOP opposition and the House Democratic leadership’s desire to avoid a vote on gun rights that Republicans would offer, Senate Democratic aides said.

So Reid agreed to use procedural maneuvers to repass the bill — with new language allowing hunting on the new public lands —in a way that will allow House Democrats to avoid the gun vote.