WASHINGTON -- Senators who support John R. Bolton to be President Bush's ambassador to the United Nations last night failed in a dramatic 56-to-42 vote to end a filibuster called because the Bush administration refuses to turn over top-secret documents related to the nominee that Democrats sought.

John R. Bolton

That blocked an up-or-down vote on confirming Bolton. The White House said Bolton eventually will be approved because he needs only 51 votes to be confirmed, and there are 55 Senate Republicans.

But ending a filibuster requires 60 votes. Now, no vote on Bolton will occur until the procedural issue is resolved, possibly next month.

Senate Majority Leader Bill Frist, R-Tenn., said he was "very disappointed" in the vote. He said it was a setback to senators working across party lines on the country's business. "It's been a very challenging week," he said grimly.

Fourteen senators reached an agreement earlier this week not to filibuster controversial judicial nominees except under "extraordinary" circumstances, but to oppose a Senate rules change that would have effectively barred filibusters on any judicial confirmations, as Frist had sought. But yesterday's filibuster on the U.N. choice was not covered by that accord.

Several Democrats involved in the earlier compromise were among the last to vote on cloture yesterday. Two signers of the deal, Sens. Mark Pryor, D-Ark., and Ken Salazar, D-Colo., voted 'no' on cloture, but two others, Sens. Ben Nelson, D-Neb., and Mary L. Landrieu, D-La., voted with Republicans to shut off debate.

Sen. Arlen Specter, R-Pa., had a prior engagement in Philadelphia and was not present for the cloture vote.

Sen. Rick Santorum, R-Pa., voted for cloture, as did Sens. Mike DeWine and George Voinovich, both R-Ohio. Sens. Robert Byrd and Jay Rockefeller, both D-W.Va., opposed ending debate.

Democrats led by Sens. Christopher Dodd of Connecticut and Joseph Biden of Delaware, insisted that they weren't filibustering against Bolton's nomination, but instead against the Bush administration's refusal to provide classified documents. "I implore the administration to provide the information," said Biden, the Foreign Relations Committee's ranking Democrat. He said the vote showed that the Senate was guarding its integrity as an equal branch of government with the executive.

Senate Minority Leader Harry Reid, D-Nev., last night said the "diversion" was not the fault of Democrats, but of the Bush administration because it refused to turn over information that senators had a right to see. He later said this was the first filibuster of the year.

After a week consumed by debates over whether filibusters against nominees were justifiable, Republicans tried to force Democrats' hand by proceeding with the Bolton vote without knowing its outcome.

From the Senate gallery, Sens. Barbara Boxer, D-Calif., and John Kerry, D-Mass., the Democrats' unsuccessful 2004 presidential candidate, as well as others engaged undecided senators in furious conversation to convince them to vote against cloture.

About halfway through the vote count, Sen. John McCain, R-Ariz., walked across the floor shaking his head -- clearly aware that Republicans lacked enough votes to carry the day.

The contested documents reveal the names of Americans stricken from raw intelligence data for privacy reasons -- names that Bolton and his staff had requested and were given by national security officials. Democrats want to know why he wanted the names; Republicans say such requests are routine.

The administration insisted that the documents were not relevant to the confirmation debate. Biden said Frist had tried for hours yesterday to get the documents but was told no by national security officials.

Bolton, 56, a blunt-spoken conservative who has been serving as the State Department's undersecretary for arms control, riled many Democrats and some Republicans first for his many attacks on the United Nations and then for his prickly personality and "bullying" manner with subordinates, and finally for allegedly trying to intimidate intelligence analysts who disagreed with him.

Bolton, a Phi Beta Kappa, summa cum laude graduate of Yale University and its law school, was previously confirmed four times by the Senate for other posts.

Yesterday's unsuccessful effort to vote on Bolton came after another long day of debate.

While Democrats said they were concerned that Bolton had wrongly exaggerated claims of progress in weapons development by Syria and Cuba, Republicans said they were impressed that he was instrumental in repealing a U.N. resolution that equated Zionism with racism and in persuading Libya to give up its nuclear program.

The only Republican who passionately argued against Bolton was once again Voinovich. It had been the Ohio senator's doubts about Bolton that kept the Senate Foreign Relations Committee from recommending his confirmation by the full Senate, meaning the nomination came to the floor without an endorsement of the nominee.

At a time when the United States is facing a loss of stature in the world, Voinovich said yesterday, sending to the U.N. post a man of "damaged credibility" was a mistake. The issue was not reform, which everyone supports, but whether Bolton will become the issue and whether the reform message would be lost, Voinovich said.

He said he was persuaded against Bolton in part because former Secretary of State Colin Powell did not sign a letter sent on Bolton's behalf by other Republican supporters. The senator said it would take more than Bolton's "sharp elbows" to reform the U.N.

Sen. Orrin Hatch, R-Utah, said he found the delay over Bolton's confirmation "dismaying" and "tawdry" and called Bolton "strong, tough, loyal" and a "decent, honorable man of inestimable intelligence."

McCain conceded that "perhaps John Bolton is not the world's most beloved manager," but he said it was time to approve the U.N. choice and get on with issues such as "saving" Social Security, passing the defense authorization bill and addressing energy needs.

Sen. Ted Kennedy, D-Mass., said, "John Bolton is more a bully than a diplomat."

In defending Bolton, whom he nominated March 7, Bush recently said, "If you're interested in reforming the U.N., it makes sense to put somebody [there] who is skilled and who is not afraid to speak his mind."