Democratic leaders are urging their rank-and-file Senators to quietly lobby the handful of uncommitted Republicans to oppose the filibuster-busting “nuclear option” as the minority party searches for the 51 votes required to defeat the proposed Republican maneuver.

Republicans, too, are furiously whipping the undecided GOP Senators to support Majority Leader Bill Frist (R-Tenn.), as both parties prepare for an unprecedented battle.

“We have asked members of our Caucus who feel a strong kinship to one of the Republican Senators to sit down and have a private conversations about this,” said Senate Minority Whip Dick Durbin (D-Ill.). “We think many of those Republican Senators respect the Senate and its tradition, and we are hoping that they will think twice about the nuclear option.”

With most Republicans and all Democrats already recording their stance on the proposal, the fate of Bush’s most controversial nominees now lie in the hands of a few centrist Republicans.

Sen. Susan Collins (R-Maine), one of the undecided centrists, said she is “hearing the usual arguments” from Democrats who are asking her to vote against the nuclear option.

But Collins said she is telling the Democrats the “same thing I am telling the Republicans: I am still studying the issue.”

It is this uncertainty that has moved political operatives to begin planning for a partisan battle that could bring business in the chamber to a screeching halt.

“Senate Republicans will be prepared to do the work of the American people if Democrats shut the Senate down,” a GOP leadership aide said.

Publicly, many Senators expressed hope that a compromise could be reached. But there is an acknowledgement from both sides that an agreement is not near.

“I don’t think we are close to a meeting of the minds,” Senate Majority Whip Mitch McConnell (R-Ky.) said Tuesday. “I think the other side has dug in.”

As of Wednesday, nothing had changed, Senators and top aides agreed.

The Senate Judiciary Committee is likely to vote out three controversial nominees today, setting the stage for a vote on the nuclear option.

Priscilla Owen and Janice Rogers Brown, both of whom are nominated for appellate court seats, faced Democratic filibusters in the 108th Congress. Terrence Boyle, who has also been nominated for an appeals court seat, is expected to face Democratic opposition when his nomination reaches the floor.

A showdown on the fate of Bush’s judicial nominees could arrive as early as next week, but it is more likely to happen the following week, aides said.

While Senators lobbied their uncommitted colleagues inside the Capitol, activities designed to put pressure on both parties continued outside the chamber.

Two pro-business Democrats, Sens. Tom Carper (Del.) and Herb Kohl (Wis.), sent a letter to three of the most influential business associations calling on them to tell Republicans to abandon the nuclear option.

The Senators cited their efforts to help shepherd class action legislation and a bankruptcy reform bill through the chamber this year, and they warned the U.S. Chamber of Commerce, Business Roundtable and National Association of Manufacturers that similar victories would not be attainable in the future if the nuclear option is successful.

“If Republicans employ the so-called ‘nuclear option,’ violating the rights of the minority, such bipartisanship would be virtually impossible,” Carper and Kohl warned.

Jim Manley, a spokesman for Senate Minority Leader Harry Reid (D-Nev.), was more blunt.

“Republicans will know the difference between a cooperative minority and an uncooperative minority,” Manley said.

Earlier in the day, several Republican freshman Senators held a news conference expressing their support for a simple majority vote to approve judicial nominees. This show of solidarity is needed, said several Republicans, who noted that if Frist is unable to convince at least 51 Republicans to support the measure, it could damage the internal comity of the GOP Conference, several senior Senators said.

“It could have a long-term effect,” said Sen. Trent Lott (R-Miss.) “This is big.”

Sen. Jeff Sessions (R-Ala.) echoed Lott’s comments, saying, “It would be detrimental to the caucus if it were to fail. I think it could be damaging to our unity, no doubt.”

Sen. John McCain (Ariz.), one of only two Republicans to publicly oppose the nuclear option, brushed off the suggestion that the defeat of this one measure would have a negative effect on Republicans’ ability to work on other legislative issues.

“We have had differences on many issues,” McCain said. “I don’t see that really being very significant.”

Sen. Larry Craig (R-Idaho) predicted that Frist would not even bring the measure up for a vote on the Senate floor unless he is convinced he has enough support to win.

“This is an issue [where] if you take it to the floor, you don’t lose — which means it doesn’t go to the floor until you know you can win,” he said. “You either win it, or you don’t go.”