Senate Republicans remain divided over the timing of calling a cloture vote on the stalled judicial nomination of Miguel Estrada, as they seek a course that will create the maximum political pressure on Democrats.

Two distinct camps have emerged in the Republican Conference’s internal debates, with an outspoken group of Senate veterans pushing for a cloture vote as soon as possible to try to break the Democratic filibuster of Estrada, according to numerous Senators and GOP aides.

But another core group, led by Majority Whip Mitch McConnell (R-Ky.) and GOP Conference Chairman Rick Santorum (Pa.), is pushing just as hard to avoid calling for the initial vote, which Republicans are certain to lose, as they have only 55 certain votes out of 60 needed to end the filibuster, which has now absorbed almost three full weeks of floor time.

In the middle sits Senate Majority Leader Bill Frist (R-Tenn.), not even two months into the job. He said Wednesday he is not ready to pull the plug on the debate and file for cloture but clearly left it on the table as an option.

“Every day I keep assessing,” Frist said, noting that Sen. Bill Nelson (Fla.) this week became the fourth Democrat to announce support for Estrada’s bid for a seat on the U.S. Court of Appeals for the D.C. Circuit. “As long as we’re making progress, there’s no need [for cloture votes]. There’s a range of opinions in the Conference, but we’re making progress.”

Democrats, however, bluntly rejected Frist’s assessment of Republican progress on gathering the 60 votes, contending that Nelson made them aware of his plans to support Estrada before the Presidents Day recess.

“We knew that two weeks ago,” Minority Whip Harry Reid (D-Nev.) said. He dared Republicans to call as many cloture votes as they liked in the days and weeks ahead, contending none of the remaining 45 Democrats would budge in their support of the filibuster.

“It doesn’t matter,” Reid said. “Everybody else has signed on for the duration.”

Republicans emerged from a Wednesday meeting of their Conference still unified in the urgent need to get Estrada onto the bench, knowing that losing Estrada to a filibuster would set a major precedent and likely pave the way for more filibusters of President Bush’s nominees.

“There’s a resolve to see this thing through,” said Sen. Lindsey Graham (R-S.C.), a Judiciary Committee member who ran for office in 2002 against Democratic efforts to stall Bush’s judges.

Sen. Trent Lott (R-Miss.), the former Majority Leader, said this week that he feels the best way to heighten the pressure on Democrats is to call a vote, putting each Senator on the record. Lott knows Republicans would lose that vote, but he said the first failed vote would be followed by a series of votes, possibly one a day on cloture for Estrada for about a week.

“At some point we’re going to have to do that,” he said. “I personally think once we have a vote, the pressure is going to build. As long as you don’t vote, everyone can hide out in the weeds.”

Some aides said this approach would give outside interest groups a sure-fire attack line on Democrats in the so-called “red” states, where Bush is very popular. Conservative groups such as the Committee for Justice, founded by GOP lawyer C. Boyden Gray, and business-friendly Latino groups have been airing ads and organizing protests in states such as Arkansas, Louisiana and Florida, targeting Democratic Sens. Blanche Lincoln, Mary Landrieu and Bob Graham, respectively.

Gray held a fundraiser at his home Tuesday night with top Bush adviser Karen Hughes and Frist as the special guests. Gray called the event a “good night” and said that his group would within days expand its ad campaign to cover five or six states, including using Hispanic stations in New Mexico to target Sen. Jeff Bingaman (D).

If Democrats were on the record voting to continue the filibuster, Lott and other Republicans — including Judiciary Chairman Orrin Hatch (Utah) — feel it will be easier for the groups to target these red-state Democrats, aides said. In addition, Bush can single them out in remarks as he travels the nation.

That course has won support from some junior Senators as well, including South Carolina’s Graham, who said Democrats are going to filibuster every single controversial judicial nominee. With so many filibusters coming, Graham said Republicans should get the Democrats on the record as supporting that tactic, then let the pressure mount.

“Unless reason prevails, I think that’s what we’ll have to do,” he said.

One GOP aide noted that there are some Republicans, including Sens. John McCain (Ariz.) and Chuck Hagel (Neb.), who appear to be pushing for a series of cloture votes and then moving on because of the pending conflict in Iraq. If fighting erupts in the next few weeks, McCain and Hagel don’t want the Senate to still be stuck debating a lower-court nomination, the aide said.

But Santorum and McConnell have been leading the charge to hold firm against calling a cloture vote, according to several GOP aides. Their contention is that no Senator casts a vote without first seriously weighing all of his or her options, and that once a vote is cast in favor of maintaining the filibuster that vote will be locked in against Estrada.

Politically speaking, McConnell and Santorum believe it’s highly unlikely a Democrat would cast a vote against Estrada and then later flip in favor of the nominee because of the pressure applied by the president and outside interest groups. Such a move could destroy a Democrat’s credibility among base voters as well as moderate swing voters.

If no more Democrats defect, Frist will be faced with a decision within the next week so that the floor can be cleared of the matter by mid-March, one GOP Senator said, guessing that an Iraq conflict could erupt by March 15.

He will either have to file the cloture vote knowing he is set for defeat on ending the filibuster or simply pull the nomination from the floor. Either way, Frist can leave the Estrada nomination on the executive calendar for future consideration, and some Republicans are privately talking about the possibility of bringing it back up in a few months if Bush has dramatically increased his domestic popularity — something that could happen with a swift victory in Iraq.