UNITED NATIONS — Questioning the Bush administration’s pro-Israel tilt, Senator Chafee, a Republican of Rhode Island, forced a delay yesterday in a key vote to confirm the nomination of John Bolton as ambassador to the United Nations.

Mr. Chafee, who supported Mr. Bolton’s nomination last year, apparently changed his mind shortly before the vote, a congressional aide who has been following the nomination battle closely said. In a fight for his political life in a tight primary election Tuesday, Mr. Chafee’s move was not totally unexpected, the aide, who spoke on condition of anonymity, said.

“It seems he decided to flip-flop on Bolton. He thought all night how to present it, and then all he could come up with was this,” the aide said, referring to a letter Mr. Chafee sent yesterday to Secretary of State Rice.

In the letter, Mr. Chafee raised questions about issues that have little to do with Mr. Bolton, Turtle Bay, or even the current Arab-Israeli situation.

The vote on Mr. Bolton’s nomination that was expected at the Senate Foreign Relations Committee yesterday was postponed and the committee’s chairman, Senator Lugar, a Republican of Indiana, declined to say when it would be rescheduled.

Ms. Rice, according to several sources, is planning to meet Mr. Chafee in an effort to convince him to support Mr. Bolton. But several Democrats, as well as some organizations close to the U.N. Secretariat, have long been lobbying against the ambassador.

A State Department spokesman, Sean McCormack, said he was “very hopeful” the Senate will conduct an “up or down vote” soon.

“Go down that list, North Korea, Iran, Sudan,” he said. “This is a real-time consequence for the Security Council, and we couldn’t have a better man up there right now than John Bolton.”

“Chairman Lugar decided to hold the vote over to a later date, and I support that decision,” Mr. Chafee wrote in his letter — although it was he who had forced the delay by changing his mind. The letter seemed designed to appeal to Arab-American voters, but the issues it raised, including perceived failures by the White House to implement the Middle East “road map,” are out of step even with the Cairo-based Arab League, which recently declared the road map “dead.”

“I don’t understand what any of this has to do with the Bolton nomination,” the executive vice chairman of the Conference of Presidents of Major American Jewish Organizations, Malcolm Hoenlein, said. Citing recent nationwide polls showing an upswing in public support for Israel, Mr. Hoenlein added that while Mr. Chafee’s positions “have long been known,” the letter shows they differ from those of most Americans. “Otherwise he wouldn’t be in such a tight race,” he said.

Recent polls among prospective Rhode Island voters show a virtual tie between Mr. Chafee and his challenger in Tuesday’s Republican primary, Mayor Stephen Laffey of Cranston.

According to the Providence Journal, Mr. Chafee is one of only two senators who received donations from the Arab-American Leadership PAC. Prominent Arab-American personalities also hosted Washington and New York fund-raisers for Mr. Chafee’s re-election campaign.

Another major Chafee contributor cited by the newspaper is the National Republican Senatorial Committee, an organization dedicated to re-electing GOP senators with the aim of maintaining the party’s thin majority in the upper house.

The Bush administration, however, was counting on yesterday’s committee vote to pave the way for easy approval of Mr. Bolton, who was named as ambassador to the United Nations last year during the Senate recess. Unless he is approved by the Senate, Mr. Bolton’s term will run out in January. Mr. Bolton’s most powerful opponent, Senator Dodd, a Democrat of Connecticut, was quoted by Reuters yesterday as saying,”I think the nomination is in deep trouble again, as it should be.”

Other Democrats have reportedly conducted a quiet campaign to lower their party’s opposition to Mr. Bolton, citing his steadfast support of Israel.

“It is no secret that I have serious questions about this administration’s policies in the Middle East,” Mr. Chafee wrote.

“Phase one of that Road Map states clearly that Israel will freeze all settlement activity,” he wrote. In the only reference to Mr. Bolton or his work at Turtle Bay, Mr. Chafee wrote, “As we tackle enormous problems in the region, most notably with Iran and Iraq, I believe we need to be successful in forging alliances. A critical part of that work is accomplished by our Ambassador to the U.N.”