Sen. Arlen Specter (R-Pa.) yesterday leapt into the procedural battling that has consumed the Senate’s Iraq debate with a proposal that would prevent majority leaders from using an arcane parliamentary move to limit amendments on contentious legislation.

Though Specter acknowledged that his plan would have little effect on the partisan standoff that has kept the Senate’s non-binding Iraq resolution in limbo, he said he long has opposed the practice known as “filling the tree.”

“It’s a very abusive practice,” the former Judiciary Committee chairman said yesterday. “Maybe abusive is too harsh a word because it’s a rule, but I’ll stand by that.”

To “fill the tree,” Senate Majority Leader Harry Reid (D-Nev.) — and past holders of his title — uses a traditional right to first recognition on the floor to introduce first- and second-degree amendments that limit rank-and-file senators’ ability to offer further amendments. Reid may fill the tree on the upcoming $463 billion funding resolution.

Unanimous consent is the central engine of the Senate, making a failure to reach agreement on which amendments will receive votes to the Iraq resolution a paralyzing development. Specter’s bill aims to secure more rights for minority-party senators but would preserve the majority leader’s recognition rights.

Specter’s support for ending the tree-filling era contrasts with his strong opposition in 2005 to the “nuclear option,” the GOP-proposed rules change to block judicial filibusters.

“There is a big difference between protecting a minority right and protecting a majority right,” Specter said. He vowed to support empowering Democrats’ right to offer amendments freely should Republicans regain control of the Senate.

Former Senate Majority Leaders George Mitchell (D-Maine) and Trent Lott (R-Miss.), now the GOP whip, hold the record for most frequent attempts to fill the tree in a single Congress, according to the Congressional Research Service. Mitchell and Lott employed the move nine times each, while retired Majority Leader Bill Frist (R-Tenn.) loaded up on amendments five times during the 109th Congress.

“I didn’t like it when Mitchell used it,” Specter said. “Frist used it a lot last year to avoid hard votes. … It’s a plague on both our houses.”

Meanwhile, the core group of seven centrist Republicans who have supported voting on a nonbinding disapproval of the president’s troop “surge” plan met with GOP leadership yesterday afternoon and sent a letter to bipartisan Senate leadership soon afterward. Sen. John Warner (R-Va.), sponsor of the leading nonbinding resolution, presented the letter on the floor.

“We respectfully advise you, our leaders, that we intend to take [Warner’s Iraq resolution] and offer it, where possible, under the standing rules of the Senate to bills coming before the Senate,” wrote Warner and Sens. Chuck Hagel (Neb.), Olympia Snowe (Maine), Norm Coleman (Minn.), Gordon Smith (Ore.), George Voinovich (Ohio), and Susan Collins (Maine).

The letter leaves the door open for the seven Republicans to try to attach the stalled resolution to the continuing resolution that must clear Congress by next Thursday or risk a government shutdown.