Senate Democrats on Monday again blocked the nomination of John Bolton as U.N. ambassador, raising the possibility that President Bush may seek to bypass lawmakers and put him in the job without a confirmation vote.

Republican leaders fell six votes short of the 60 votes needed to end a procedural hurdle known as a filibuster and advance the nomination to a confirmation vote.

The Senate vote of 54-38 to try and overcome the filibuster came after Bush called for an immediate up-or-down vote on Bolton’s nomination.

“We’ll, put him in. If they’re interested in reforming the United Nations, they ought to approve John Bolton,” Bush said at a news conference with European leaders.

It was the second failed attempt by Senate Republican leaders to bring the contested nomination to a vote. The White House would not rule out the possibility Bush could appoint Bolton to the post during an upcoming congressional recess.

“It is critical that we get him in place,” said White House spokesman Scott McClellan.

But Senate Republicans raised concerns about a recess appointment

Sen. Pat Roberts, a Kansas Republican who heads the Senate Intelligence Committee, said the country would be better served by a U.N. Ambassador who was confirmed by the Senate.

Appealing again for a confirmation vote on Bolton, Roberts said, “I hope that people will take a little longer look at our national interests and say that let’s not go down the road to a recess appointment.”

Sen. George Allen, a Virginia Republican, said it was a “legitimate concern” that Bolton would be seen as damaged goods and lack credibility if he is appointed rather than confirmed.

“I would hope that the president will stand by John Bolton and keep fighting for him,” Allen said.

Democrats are demanding that the White House release information they say is important to the Senate’s review of his fitness for the job. They want to know whether Bolton, the top U.S. diplomat for arms control, misused intelligence and bullied analysts who did not conform to his hard-line views.

Sen. Christopher Dodd of Connecticut, a member of the Foreign Relations Committee charged the administration has “stonewalled” Democrats’ efforts to get the information.

Dodd also cautioned against a recess appointment, noting that Bolton he would be the first U.S. nominee not confirmed by the Senate ever to go to the United Nations.

White House Chief of Staff Andrew Card talked to Sen. Joseph Biden of Delaware, the top Democrat on the Senate Foreign Relations Committee about providing additional information on Bolton, but a source familiar with the discussions said they came to no agreement.

After the Senate action White House spokesman Erin Healy said Bush still wanted a confirmation vote. “It’s unfortunate the Senate Democrats continue to play partisan politics with his nomination,” he said.

Bolton, a fierce critic of the United Nations, is a favorite of conservatives. Bush and his Republican allies in the Senate see him as the right man to press for U.N. reforms.

Bush has on occasion issued recess appointments to sidestep Senate opposition to his nominees. He could do so for Bolton during the week-long Fourth of July holiday recess or during Congress’ month-long August break.

A recess appointment for Bolton would allow him to serve as ambassador until a new Congress is seated in January 2007.