WASHINGTON — Britain’s ambassador to America has sought to reassure the Bush administration that Prime Minister Brown values the alliance with America, ahead of a Camp David summit that is set to mark a shift in the “special relationship.”

Mr. Brown is due to be received by President Bush on Sunday night before flying to New York on Monday, where he is expected to visit the United Nations and meet Secretary-General Ban.

The Daily Telegraph has learned that some senior American officials have expressed dismay over signals from Mr. Brown — principally the appointment of Mark Malloch Brown, an outspoken critic of Mr. Bush, as a foreign office minister — that he might take a different approach to the special relationship to that taken by Prime Minister Blair.

David Manning, the British ambassador in Washington, telephoned Secretary of State Rice and National Security Adviser Stephen Hadley to stress the value Mr. Brown places on ties with America.

But the U.N. trip is a clear sign that the prime minister, although a frequent visitor to America and admirer of its economy, will place a premium on multilateral relationships as well as the trans-Atlantic alliance.

There is little incentive for Mr. Brown to develop a close, personal link with Mr. Bush, who is due to leave office in 18 months and whose popularity ratings recently dipped to 25%.

A former British diplomat said, “Brown is not going to be looking to Washington for his spiritual guidance and instructions. It’s not that he’s anti-American or looking to radically overhaul British policy, but there’s going to be a significant change in tone and emphasis.

“The fact that Malloch Brown is in the senior echelons of decision-making is significant. It’s not for nothing that he was brought into the government. Under Brown, there won’t be any of the instinctual, shoulder-to-shoulder stuff there was with Blair.”

Some British officials had considered delaying a Bush-Brown meeting until September. But jitters over a recent speech in Washington by International Development Minister Douglas Alexander and outspoken comments by Mr. Malloch Brown ensured plans were brought forward.

Mr. Alexander hailed the virtues of “soft power,” calling for “new alliances, based on common values, ones not just to protect us from the world, but ones which reach out to the world,” and an end to a country’s might “being measured in what they could destroy.”

In the context of a speech on international development, Mr. Alexander’s comments were unremarkable, but in briefings to the press in London, they were portrayed as a distancing from the Bush administration.

After a rash of headlines about a breach in the “special relationship,” Mr. Manning called Ms. Rice and Mr. Hadley to tell them that the speech had been misinterpreted.

But the situation was exacerbated when Mr. Malloch Brown, a former U.N. deputy secretary-general, told the Daily Telegraph that British foreign policy should “become much more impartial” and that it was unlikely Mr. Bush and Mr. Brown would be “joined together at the hip like the Blair-Bush relationship.”

The appointment of Mr. Malloch Brown, widely viewed within the Bush administration as anti-Bush, had already raised concerns among senior American officials.

The prime minister moved swiftly to quell the notion that he wanted to loosen Britain’s ties with America, instructing his chief of staff to write to Cabinet members reminding them of his insistence that “we will not allow people to separate us from the United States in dealing with the common challenges we face.”

Foreign Secretary David Miliband publicly reprimanded Mr. Malloch Brown, saying, “He’s been given a very specific job to do by Gordon Brown, he’s been asked to work on Africa, on Asia and on U.N. reform.”

A White House spokesman said, “The president and the prime minister have reaffirmed the close bond between the U.S. and U.K. and agreed to continue a strong and cooperative relationship.”