WASHINGTON — The Senate yesterday refused for a second time to confirm John Bolton as U.S. ambassador to the United Nations, prompting his supporters to urge President Bush to bypass Congress and give the controversial nominee a recess appointment, which would last 18 months.

The vote was a setback for Bush, whose party controls the Senate, and it was the latest in a string of partisan impasses that also have stymied his efforts to appoint judges and restructure Social Security. Some senators said an appointment while Congress is in recess now appears to be Bolton's only hope, even though it would be politically contentious and would send him to the United Nations under a cloud. That action could come as early as July 2.

Republicans denounced Democrats as obstructionists after yesterday's vote. But Democrats said Bush deserves the blame for tapping a nominee known for his combative style and criticism of the United Nations and then rejecting lawmakers' requests for documents related to his tenure at the State Department.

The Senate voted 54-38 to end debate on Bolton's nomination. That was six votes short of the 60 needed in the 100-member chamber to stop filibusters. The vote suggested that Bolton has gained no ground since May 26, when 57 senators voted to end the filibuster before one switched for parliamentary reasons.

Sen. George Voinovich, R-Ohio, joined 37 Democrats in voting against cloture yesterday. The three Democrats who voted to end debate May 26 did so again: Mary Landrieu, La.; Ben Nelson, Neb.; and Mark Pryor, Ark. Eight senators did not vote, including Republicans John Thune, S.D.; Norm Coleman, Minn.; and Conrad Burns, Mont.

Several senators said Bolton could have won a simple confirmation vote if the filibuster had been ended. With no sign of a compromise between Democrats and the White House over the disputed documents, however, several lawmakers said they saw no strategy that would pick up the half-dozen votes needed to end debate and allow a confirmation vote.

A senior White House official said last night that Bush will continue to press for a confirmation vote but has no plans for compromising on documents and is considering a recess appointment.

"It's time for the Senate to give an up-or-down vote now," Bush said at a news conference with European Union leaders before the Senate vote. "If they're interested in reforming the United Nations, they ought to approve John Bolton."

White House spokesman Scott McClellan did not rule out the possibility of a recess appointment but said, "We continue to urge the Senate to let him have an up-or-down vote on the floor."

The prospect of a recess appointment for Bolton infuriates Democrats.

The Constitution gives the president "power to fill up all vacancies that may happen during the recess of the Senate, by granting commissions which shall expire at the end of their next session." Historians note that Congress in the 18th century met only for three-month sessions and that the president needed latitude to fill executive or judicial vacancies when Congress wasn't at work.

Few presidents made such appointments before the 1940s. They since have become common, although constitutional scholars have questioned whether they are appropriate in midsession.

Bush's most controversial recess appointment came in February 2004, when he named William Pryor to the 11th Circuit Court of Appeals in Atlanta after Senate Democrats blocked his confirmation.

That appointment was challenged in court, but the Supreme Court refused to hear the case in March. Still, in a statement issued with the decision, Justice John Paul Stevens warned that the issue wasn't settled.

Opposition to Bolton, a former undersecretary of state for arms control, originally centered on his sharp criticism of the United Nations and his upbraiding of subordinates who differed with him on foreign policy. Over time, however, Senate Democrats focused on the administration's refusal to provide documents they said were needed to assess Bolton's fitness for the job.

Democrats wanted to test Bolton's claims about his role in preparing disputed testimony about Syria in 2003. They also demanded information related to his access to details from secretly intercepted conversations of foreigners and, in some cases, U.S. citizens. Democrats have asked whether Bolton was seeking secret information on rivals in the U.S. intelligence and foreign-policy communities.

The administration repeatedly has said the Senate did not need the documents to determine Bolton's fate and accused Democrats of stalling. The White House made an 11th-hour bid yesterday to break the impasse. Chief of staff Andrew Card asked whether providing the Syria-related documents would satisfy Democrats, according to a Democrat familiar with the exchange.

But Delaware Sen. Joseph Biden, the Foreign Relations Committee's top Democrat, said it would not, reiterating his party's demand for all the intelligence intercepts Bolton had requested as well, Senate sources said.

Bush strategists believe the president may benefit from the fight because most Americans distrust the United Nations and want changes. GOP strategists see no downside to a recess appointment other than that Democrats would protest it and redouble efforts for the courts to intervene to prevent the practice.

"The American people know why I nominated him, because the U.N. needs reform, and I thought it made sense to send a reformer to the United Nations," Bush said before the vote. "The U.N. is an important organization, and the American people ... understand how important it is when the U.N. is reformed and is held to account."

Post reporter Dafna Linzer contributed to this report; background on the past use of recess appointments was provided by Knight Ridder Newspapers.