LONDON - Britain, America's staunchest ally in Europe, joined in the widespread expressions of disappointment yesterday over the U.S. repudiation of the new International Criminal Court but said it would use its close trans-Atlantic ties to try to change Washington's attitude.

"What we are involved in is a very detailed and active conversation with the U.S., trying to allay their fears," said Foreign Secretary Jack Straw. "We do not share their view about this."

The object of the Europeans' concern was the U.S. veto Sunday of a Security Council resolution extending the United Nations peacekeeping mission in Bosnia. The measure was supported by the other members, most notably Britain and France.

Denmark assumed the six-month presidency of the European Union yesterday and led the chorus of criticism of the U.S. move. "I deeply regret this dramatic step that threatens U.N. peace operations in general," said the country's foreign minister, Per Stig Moller.

Carl Bildt of Sweden, a former envoy to the Balkans for the European Union and United Nations, called the Bush administration decision "a very dangerous exercise in diplomatic brinkmanship, with possible consequences that no one is fully aware of."

The United States cast its veto after its demand to put U.S. peacekeepers beyond the reach of the new International Criminal Court was rejected, then agreed to a three-day extension to give all sides time to seek a political solution.

"I understand the concerns of the United States of America; they are perfectly legitimate concerns," Prime Minister Tony Blair told Parliament. "Our view, however, is that they are met."

Blair has strongly emphasized Britain's close relations with Washington and has used them to try to enhance his country's standing in Europe.

But yesterday's divergence is just one of a growing number testing ties between Washington and London. Britain has vigorously objected to U.S. tariffs on steel imports. Last week, the British made it clear they did not agree with Bush's call to replace Yasser Arafat as Palestinian leader.

Britain is also a vocal supporter of the Kyoto treaty on eliminating greenhouse gases, which the United States has refused to ratify. But Blair said yesterday that these disagreements would not shake Britain's links with the United States, which he called the "foundation stone" of Britain's foreign policy.

In Brussels, Belgium, the European Commission spokesman, Gunnar Weigand, said the United Nations had asked European nations to consider taking over the police-training task force in Bosnia if the United States refuses to extend its mandate for the mission.

Comments elsewhere reflected growing irritation with the United States for pursuing policies at odds with allies and appearing content to go it alone.

"What's important now is to replace the power of might with the power of right worldwide, and the United States can't always stand aside," said Germany's justice minister, Herta Daubler-Gmelin.

Dominique Moisi, a leading French political analyst, said the U.S. rebuke of the court was motivated by arrogance and irresponsibility. "Arrogant because they are placing themselves outside and above the law," he said. "And irresponsible because one day they will need a world in which they, too, belong."