Sen. Robert Byrd (D-W. Va.) has begun to take a more active role in defending Democratic filibusters of judicial nominees, preparing to become a major floor presence if the GOP tries to invoke the “nuclear option” later this spring.

Byrd, widely regarded as the Democrats’ top parliamentary expert, has taken umbrage with recent GOP attempts to cite his maneuvers as Majority Leader in the mid-1970s as the precedent for its possible attempt to unilaterally end filibusters on judicial nominations.

Byrd convened a meeting of at least nine Senate Democrats in his Appropriations Committee suite just before the week-long recess began, explaining how he believed the situation in the 1970s was different and how he will fight the GOP attempts this time around, Democratic aides said.

While no specific role for Byrd has been set in the judicial battles, his entry into the debate marks a serious turn for Democrats as they prepare to mount a vigorous defense of the filibuster — a tactic they view as their last defense against complete GOP control of Washington.

“At the heart of the United States Senate is the right to amend and the right to debate,” said Tom Gavin, Byrd’s spokesman. “When he sees a danger to it, he’s not going to sit idly by.”

In the judicial fights of recent years, Democrats have been led by their leadership and senior members of the Judiciary Committee, including Sens. Patrick Leahy (D-Vt.), the ranking member, and Edward Kennedy (D-Mass.), a former chairman of the panel.

Byrd, the ranking member of Appropriations, has generally deferred to those Senators. He has been supportive of all 10 filibusters Democrats mounted against appellate court nominees of President Bush in the 108th Congress.

But Byrd took the latest effort by Republicans personally, said one senior Democratic aide, citing a law review article by former GOP leadership aide Marty Gold as the development that pushed Byrd to get involved in the debate over judges.

In a 68-page article for the Harvard Journal on Law and Public Policy, Gold and co-author Dimple Gupta, a former Justice Department official, cite Byrd’s role in the long effort to change rules and lower the threshold for invoking cloture from two-thirds of the Senate to 60 votes, culminating with a deal in 1975 when Byrd was Majority Leader.

Democratic aides said Byrd believes Gold, who served as a top parliamentary expert for former Majority Leader Howard Baker (R-Tenn.) in the 1980s and for Majority Leader Bill Frist (R-Tenn.) in 2003 and 2004, misstated Byrd’s attempts to change the rules, which included threats of changing the rules on a simple majority vote.

Gavin declined to comment on what specifically drove Byrd to get involved in the judicial fight, but he acknowledged that the Senator’s longstanding role as a parliamentary expert was a main draw. He would not say what steps Byrd would take as retribution if the Republicans were successful in changing the rules unilaterally, although he said Byrd intends to “raise the alarm” as the battle draws closer.

“He’s certainly been looking at this for many, many weeks,” Gavin said.

Other Democratic aides emphasized that Byrd’s role would likely be similar to the one he has taken in opposing the war in Iraq. He will become one of the primary floor speakers in opposition to any change of the filibuster rule, making long, extemporaneous speeches that pillory the administration. Byrd, 87, is not considered a leader for Democrats in delivering the party’s message at press conferences or on the political TV talk shows.

Republicans have not said when or if they would launch the “nuclear” option to end filibusters. Democrats have warned that the move would be met with a near termination of other legislative business in the chamber.

This week, Judiciary Chairman Arlen Specter (R-Pa.) begins the first round of nomination hearings with two filibustered hold-overs from the 108th Congress: William Myers for the 9th U.S. Circuit Court of Appeals and Terrence Boyle for the 4th Circuit.

Specter said last week that he had not taken a position on the nuclear option — although after preserving his chairmanship in November following a two-week battle with conservatives over his view of abortion, he seemed to indicate that it was an acceptable move by Republicans to end Democratic filibusters.

Then, last week, Specter clearly spelled out his desire not to make the move because of the likely Senate stalemate that would result. “It would likely be bedlam in the Senate,” he said.

Democrats pounced on Specter’s latest comments as an example of continued resistance from within the GOP Conference to the unilateral rule change, which Republicans prefer to call the “constitutional option” because it would involve getting a ruling from the chair that filibusters on judicial nominees were unconstitutional.

Such a ruling would require just a simple majority to be upheld.

One Democratic office has compiled a war-room-style chart, using an Excel spread sheet, to document every public utterance by a Republican Senator that shows the lawmaker’s support of the nuclear option to be at least ambiguous.

The chart cites at least 16 Republican Senators as having expressed wariness about the potential rule change, including moderates like Specter and Olympia Snowe (Maine) and conservative mavericks such as John McCain (Ariz.) and Chuck Hagel (Neb.).

No votes on judges are likely until after the two-week spring recess, with the chamber back in session April 5. Given the April 15 statutory deadline for completing the budget as well as a nearly $82 billion supplemental spending bill on Iraq issues, those items will also take precedence over judges, senior GOP aides say. The next showdown over judges might not come until well into April or early May.