Sen. Joe Lieberman (I-Conn.), a sponsor of the measure, said he was “deeply disappointed and deeply outraged” by the failure, but remained optimistic.

The bill achieved the majority with a vote largely along party lines Tuesday, but fell three votes short of the number needed for cloture.

D.C. Del. Eleanor Holmes Norton (D) and Mayor Adrian Fenty (D) lobbied Republicans on the Senate floor moments before the vote. Norton said Republicans dealt with “almost unprecedented pressure” to filibuster.

Eight Republicans voted for cloture, but Sen. Max Baucus (D-Mont.) voted against it, believing expanding the size of the House would “dilute” Montana’s influence in Congress.

“It's also a slippery slope,” Baucus said in a statement Tuesday. “If we expand the playing field now, then who is to say where it will stop? Will we give votes to territories, protectorates and commonwealths? This measure just doesn't make sense.”

The Republicans who voted for the bill were Sens. Bob Bennett (Utah), Norm Coleman (Minn.), Susan Collins (Maine), Orrin Hatch (Utah), Richard Lugar (Ind.), Olympia Snowe (Maine), Arlen Specter (Pa.) and George Voinovich (Ohio).

Sen. Robert Byrd (D-W.Va.), who backs full voting rights for the House and Senate, did not vote. Byrd has constitutional concerns with the bill, and favors a resolution that would amend the Constitution.

Senate Majority Leader Harry Reid (D-Nev.) expressed his disappointment, saying citizens who pay taxes, serve on juries and fight in the armed services should be given a voting member of the House.

“If we can send D.C. citizens to fight for democracy in Baghdad and ensure Iraqis have the opportunity to vote, the least we can do is give the same opportunity to our fellow Americans," Reid said.

Ilir Zherka, executive director of DC Vote, said this was the first filibuster of a voting rights bill since the era of segregation.

"We are outraged that a minority of senators, led by Senators Mitch McConnell and Trent Lott, prevented the majority from voting on our bill. McConnell and Lott chose to filibuster a bill extending democracy at home at a time when they are pushing for democracy in Iraq,” Zherka said.

Minority Leader Mitch McConnell (R-Ky.) said the bill is unconstitutional because the Constitution limits membership in the House to the states and thus excludes the District.

McConnell encouraged citizens to amend the Constitution in order to gain the seat.

“If the residents of the District are to get a member for themselves, there remains a remedy: Amend the Constitution,” he said in a floor statement Monday.

Sen. John McCain (R-Ariz.) also voted against cloture. “I come down on the constitutionality side of it,” he said.

Most GOP presidential candidates have not taken a position on the measure. However, former Arkansas Gov. Mike Huckabee (R) recently said he backs it.

Sen. Orrin Hatch (R-Utah), a co-sponsor of the bill, said the measure deserved to pass to give citizens voting rights. “Frankly, if it’s so unconstitutional, then what does the other side have to fear?” he said. “We’re prepared to accept whatever the Supreme Court says.”

The legislation would have also given the conservative state of Utah an additional House seat.

The bill’s supporters said they will continue to push for passage, even though President Bush has vowed to veto the measure.

Rep. Tom Davis (R-Va.), who co-sponsored the House bill that passed earlier this year, expressed optimism: “A majority of senators saw the wisdom of granting full voting representation in the House for District residents. We're knocking on the door. We'll be back.”

Norton agreed, saying, “The fat lady has not sung yet. This war is not over.”

Elana Schor contributed to this article.