As Senate Majority Leader Bill Frist announced his intention to file a cloture petition to end debate on the Priscilla Owen (search) nomination, the behind-the-scenes effort to strike a filibuster deal continued.

"The principle is that judicial nominees with support of a majority of United States senators deserve a fair up-or-down vote on the floor of the United States Senate," Frist said early in the day.

That petition would require a vote to end debate on Tuesday. If the vote fails — meaning Republicans don't achieve the 60 votes necessary to break the Democratic filibuster — the stage will be set for a showdown vote on Tuesday to abolish judicial filibusters, the so-called "nuclear option."

Before that showdown occurs, however, moderate lawmakers were working furiously Thursday to hammer out a compromise that would avoid triggering the "nuclear option." Some negotiators said Thursday evening that they're as close as they've been to achieving it.

Late Thursday, Sen. Kent Conrad (search), D-N.D., said he expects no talks on Friday as some members have family graduations and other events to attend this weekend.

In a meeting in Arizona Republican Sen. John McCain's (search) office, members involved in talks said Thursday they plan on "shopping around" the latest compromise language.

"I still think we're making progress ... we're going to take a little time to reflect and talk amongst ourselves and come back in an hour, hour and a half to see where we are," said Sen. Mark Pryor, D-Ark., who added, "We're as optimistic as we've been."

Earlier in the day, Sen. Ben Nelson, D-Neb., said that the "situation is very fluid" and the options include either a quick conclusion or no deal at all.

"Sometimes these negotiations and these consultations and meetings seem endless but you're not able to really judge how long something's going to take," Nelson told FOX News later Thursday. "I don't know if you're going to have it within the next hour or at all, but you've got to continue to talk and work through language and work through concepts."

Nelson told FOX News that the group of senators have "fairly sophisticated ideas" down on paper and that some of those ideas "could be abolished ... some could be reconstructed ... edited ... each word is very important" so that there's no wiggle room for interpretation.

Watch the latest update on the filibuster fight from FOX News by clicking in the video box.

Democrats argue that doing away with the filibuster has drastic ramifications and that it must be retained to give the minority a debate tool to voice dissent.

"The Senate is not a rubber stamp for the executive branch," Reid said on the Senate floor, when arguing that President Bush and the GOP were trying to "rewrite the Constitution and reinvent reality" in their push to confirm controversial judicial nominees.

He added: "We're the one institution where the minority has a voice and the ability to check the power of the majority. Today, in the face of President Bush's power grab, that's more important than ever."

Building the 'Trust Factor'

Frist and Reid opened formal debate on Owen Wednesday and continued Thursday. The Texas jurist's nomination is considered a test to the Democrats' ability to continue blocking judges with filibusters. Owen is up for a position on the 5th U.S. Circuit Court of Appeals in New Orleans.

Sen. David Vitter, a freshman Republican lawmaker from Louisiana, is one of several senators who protested the use of the Democrats' judicial filibuster, which he said has "ground everything to a halt." Vitter said he got a good feel for what his constituents think of such Senate impasses while he was campaigning around the state last year.

"What I heard over an over and over is that we need to do the people's business, we need to move beyond this bitter partisanship and obstruction and do the people's business. Give these people an up-or-down vote then move on to key issues like energy," Vitter told FOX News.

"What Democrats want to do is forestall the results of the election … we have elections in this country for a reason — to put people in office and allow them to govern."

At a news conference outside the Capitol, Frist and others called treatment of Owen and Janice Rogers Brown, a California Supreme Court judge whom Bush has named to the federal appeals court, "unnecessary, uncivil. It is injustice.

"I pledge to you here today that I will do everything in my power to see that it stops," Frist said.

Bishop Harry Jackson, chairman of a group of black pastors, called Brown "not only a legal hero for black America, she is a legal hero for all America."

"Why are they afraid to put a black woman on the court?" Jackson asked.

At the same time, however, members of the Congressional Black Caucus released a letter to Frist arguing that his call for a partial ban on judicial filibusters "would be particularly offensive to people of color."

There was irony — as members of the caucus noted — since the historic civil rights legislation of a half-century ago was passed only after supporters overcame filibusters by conservative Southern Democrats and like-minded Republicans.

"The filibuster was systematically used when Senate minority rights meant the denial of the rights of African-Americans," caucus members wrote. "We cannot and will not stand down when Senate minority rights are proposed to be overruled against a Senate minority that seeks to protect the rights of African-Americans."

Minority Exercises Muscle

The Democrats' move is an effort to show Republicans that they are more than willing to make good on grinding Senate business to a halt if the so-called "nuclear option" (search) was employed, which means the use of judicial filibusters will be banned.

Because Democrats already have prevented final votes on 10 of Bush's first-term appeals court nominees, and have threatened to do the same this year to seven the president has renominated, Republicans are considering doing away with the filibuster — or endless debate — in order to get things moving in the chamber and get an up-or-down vote on the nominees. The filibuster can be overcome only by a majority of 60 votes or more in the 100-member Senate.

But most lawmakers want to avoid the nuclear option altogether so hope on a deal remains. However, in that deal, Democrats say they want to reserve the right to filibuster a judicial nominee under what they deem "extraordinary circumstances." Nelson said Thursday that senators have reached a general comfort level in what is defined as extraordinary circumstances.

Nelson said the biggest progress throughout the course of these talks is the building of trust but noted that a few senators who weren't present at Wednesday's talks, such as Democratic Sens. Robert Byrd of West Virginia and Conrad, were in the negotiating room Thursday.

"You build your trust in these [negotiations] ... and I think that's been an improvement since day one ... the trust factor is increasing ... but this is a difficult negotiation ... each side is giving up something," Nelson told FOX News.

While Bush has made clear he wants an up-or-down vote for all his judicial nominees, a White House source told FOX News "there is no active lobbying" on behalf of the president in the rules debate. Such lobbying, the source said, could lead to a "huge outcry" by Republicans as well as Democrats that the executive branch is trying to affect a Senate rules change. The source said, "It would not be productive to getting an up-or-down vote for the president's nominees."

Prelude to Supreme Court Fight?

"This whole debate, for me, is about the Supreme Court," said Sen. Lindsey Graham, R-S.C., one of the negotiators. "What do you do with the next level? Can you get the Senate back to more of a normal working situation?"

While lower court nominees are at the forefront of the argument, the clear subtext of the debate is how the Senate will treat a future Supreme Court nominee from Bush.

"The attempt to do away with the filibuster is nothing short of clearing the trees for the confirmation of an unacceptable nominee to the Supreme Court," said Democratic leader Harry Reid. He accused the president of an attempt to "rewrite the Constitution and reinvent reality" with his demand for a yes-or-no vote on all nominees.

While the Supreme Court has no current vacancies, court watchers expect a retirement before the end of Bush's presidency. Chief Justice William Rehnquist (search), who is 80, is fighting thyroid cancer, and some analysts are taking odds that he could make a statement as early as this summer.

"When a Supreme Court position becomes open the issue will be, will it require 60 votes to approve a Supreme Court judge — something that's never required — or will it be a majority vote? Must we have a super majority?" said Sen. Sam Brownback, R-Kan.

One of the deals being worked on would have the Senate confirming Owen, California judge Janice Rogers Brown (search) — a California Supreme Court justice nominated to the Circuit Court of Appeals for the District of Columbia — and former Alabama Attorney General William Pryor (search), with Idaho lawyer William Meyers' (search) nomination scuttled. As part of that deal, two Michigan nominees, David McKeague (search) and Richard Griffin (search), would be confirmed, while a third nominee — Henry Saad (search) — would be jettisoned.

A fourth Michigan judge, Susan Neilson (search), also would be confirmed. She has not been filibustered by Democrats in the past.

Senators are still negotiating that part of the deal and it is subject to change, aides said.

Under the latest Republican-crafted proposal, both sides would have to operate on "good faith." Republicans would be bound not to ban judicial filibusters only if Democrats forswear judicial filibusters except for extraordinary situations, aides said.

But that plan doesn't sit well for some.

"I don't like that plan at all because I think that's where we're deciding who's going to get a vote and who's not," Sen. Richard Shelby, R-Ala., told FOX News Thursday morning. "I believe all of these nominees — they've been vetted, they've come out of committee, they're extremely qualified and we ought to vote them up-or-down."

The Senate has approved 208 Bush judicial nominees (search), including 35 appeals court judges.

Just a majority of senators present are needed to approve a nominee once a vote is called in the Senate, and only 50 if the vice president, who breaks ties, votes in favor of a nominee.

FOX News' Julie Asher, Wendell Goler, Molly Hooper and Liza Porteus and The Associated Press contributed to this report.