WASHINGTON ? Seven Republican senators will determine the outcome of a showdown this week between the president and Congress ? and a minority within it ? over who is going to shape the federal courts.

Barring any unforeseen developments, these are the lawmakers in the make-or-break position when it comes to deciding whether to allow a Senate minority to block a president’s nominees for the federal bench.

The senators are Susan Collins of Maine, Chuck Hagel of Nebraska, Arlen Specter of Pennsylvania, John Warner of Virginia, Mike DeWine of Ohio, Lisa Murkowski of Alaska and John Sununu of New Hampshire.

At issue is an effort by Senate Majority Leader Bill Frist to ban judicial filibusters. The Senate’s Democratic leader, Harry Reid of Nevada, wants the ability to block nominees for the Supreme Court and lower courts whom his party views as outside the legal mainstream.

The seven Republicans have not committed publicly to supporting either Senate leader.

All 44 Senate Democrats, joined by independent Sen. Jim Jeffords of Vermont and three Republicans, have said they oppose curtailing a Senate minority’s ability to block the president’s judicial nominees with just 41 votes in the 100-member Senate.

Frist, R-Tenn., has 45 of the Senate’s 55 Republicans on his side.

During President Bush’s first term, Democrats succeeded in blocking 10 of his judicial picks. Both Bush and Frist are making the case now that it should take only a simple majority ? 51 votes, rather than 60 now ? for a nominee to win confirmation for a lifetime appointment to a federal appeals court or the Supreme Court.

For Democrats to prevail, they need the support of three of the seven undecided Republicans. Frist needs five votes from five of those Republicans so Vice President Dick Cheney could have the chance to break a tie in favor of Bush’s position.

Frist said Friday he will bring up the first of the blocked nominees ? Texas judge Priscilla Owen and California judge Janice Rogers Brown ? this week.

Some of the seven Republicans, including Collins, have made up their mind but are not saying how they will vote. Warner and others say they have yet to decide ? and hope they will not have to.

“I’m always working on the issue,” Warner said last week. “I’m hopeful the leaders can reach a compromise. I’m optimistic we can reach a compromise.”

So far, only Republican Sens. John McCain of Arizona and Lincoln Chafee of Rhode Island have broken party ranks, expressing concern about a change that could permanently reduce minority rights in the Senate. Vote counters in each party say Republican Olympia Snowe of Maine also is likely to side with Democrats.

Democrats insist there are other Republicans who support the Democratic position but do not want to say so publicly. Republicans note that all the other GOP senators who started out publicly uncommitted ? Thad Cochran of Mississippi, Ted Stevens of Alaska and Richard Lugar of Indiana, for example ? now side with Frist.

Warner is the last of the powerful GOP “old bulls” in the Senate not to say he will join with Frist. Warner has said repeatedly that he worries that ending the judicial filibuster will weaken the Senate.

“I tend to be a traditionalist, and the right of unlimited debate has been a hallmark of the Senate since its inception,” Warner said. “Without question, though, I am strongly opposed to the use of the filibuster to block judicial nominations.”

Liberals and conservatives are focusing on Warner and other undecided Republicans through telephone calls, Internet campaigns and television advertisements.

Conservative groups such as Progress for America and Focus on the Family have spent millions of dollars on ads since mid-April in Alaska and elsewhere trying to persuade undecided Republican senators to support Frist.

Murkowski said those efforts have backfired with her.

“I was very offended at the tone,” Murkowski said. “But they’ve continued, and it’s been kind of interesting. I’ve probably gotten more positive feedback for my position, which Alaskans consider to be very thoughtful, very deliberate, about what is happening here in the Senate.”

The liberal group People for the American Way says Murkowski is “the last defense against an attack on our Constitutional checks and balances.”

“Alaska counts on Senator Murkowski to do the right thing. Now, the whole country is counting on her,” according to an ad that the group plans to run this week. The $1 million television campaign also will mention Snowe and Collins in Maine and Specter in Pennsylvania.

DeWine sees power in not having committed to either side.

“I’ve decided. I just haven’t announced it yet because I think that it’s a good chance that we can get it worked out,” DeWine said. “I’m hopeful that by not announcing it, I can help keep these negotiations going.”

One option for the undecided senators could mean joining with Sen. Ben Nelson, D-Neb. He is trying to convince 12 Republicans and Democrats that they should block Frist from banning judicial filibusters and also stop Reid from filibustering all of Bush’s contentious nominees.

In the end, Murkowski said, the question has to be about the Senate, not politics, the president or the party.

“We have to remember that our decision has to be in the best interest of the institution as a whole,” Murkowski said. “Not in the best interest of the Republicans, not in the best interest of the Democrats, but in the best interest of we as senators and the institution itself. I think that’s what we should keep in mind.”