On one side there was emollience, restraint and an emphasis on diplomatic approaches to international crises, especially in the present stand-off with Iran. On the other were apocalyptic warnings, belligerent talk and a confrontational approach with the West’s potential enemies.

The odd thing was that, for once, it was Europeans who took the most confrontational line and the most unlikely Americans who emphasised calm and diplomacy.

Frau Merkel, in a blunt and pugnacious speech, attacked the Iranian Government for pressing ahead with its nuclear programme in defiance of international opinion.

Using a rhetorical device often employed by Americans to justify pre-emptive action, she said that Adolf Hitler could have been stopped in the 1930s if the world had taken stronger action against him sooner. And she denounced the recent inflammatory remarks made about Israel by President Ahmadinejad of Iran.

“A president that questions Israel’s right to exist, a president that denies the Holocaust, cannot expect any tolerance from Germany,” she said. Indeed, she clashed with Abbas Araghchi, the Iranian Deputy Foreign Minister, who defended his country’s actions in response to the decision by the International Atomic Energy Agency to refer Iran to the UN Security Council.

When he gave warning that Iranian law required the country to suspend all co-operation with the international community, Frau Merkel replied: “Then you might need to consider changing your laws.”

Mr Rumsfeld, by contrast, was a model of diplomatic behaviour. He praised the alliance’s historic achievements and said that the United States favoured a negotiated solution to the Iranian crisis. “We must continue to seek a diplomatic solution to stopping the development of its uranium enrichment programme,” he said.

The strange reversal of roles was another example of the improved relationship between the US and Europe in the past year, driven in part by a more conciliatory US foreign policy and, in recent months, by the political changes in Germany.

There was almost no discussion of Iraq, the subject that has caused such anger here in the past few years. Instead there was an emphasis on shared values and goals.

And yet, beneath the undoubted improvement in the rhetoric, the hard reality of policy may still pose serious potential differences along more familiar lines in the near future.

Frau Merkel, despite her tough talk, insisted that the Iranian crisis could be resolved only by negotiations, not military action.

And while Mr Rumsfeld was conciliatory, John McCain, the Arizona senator, said that the US must keep open the military option against Tehran.

Mr McCain, in characteristically blunt form, once again demonstrated his willingness to outflank the Bush Administration as an advocate for a hawkish foreign policy.

He kept up the pressure on Iran and attacked the Russian Government of President Putin for its repressive domestic and threatening international policies. He also said that the other G8 leaders should consider boycotting the meeting scheduled to be held in St Petersburg this summer.

With Mr McCain emerging at this early stage as the front-runner for the Republican nomination for the US presidency in 2008, it was an intriguing potential preview of the direction of US policy in the next few years, and a sign that transatlantic tension may be more durable.

And yet, in a powerful example of Mr McCain’s ability to appeal to a broad political spectrum at home and abroad, the senator was praised by the Europeans at the conference for his stand in the US Congress against torture.

On Saturday night, to the strains of Mozart in the baroque splendour of the Bavarian Minister-President’s residence, the independent-minded US senator was presented with a special medal celebrating “peace through dialogue”.

It will take a far more significant change in the transatlantic relationship before Mr Rumsfeld — who had, diplomatically, already left for Washington by then — receives such a European honour.

Times Recommends

• Air crash: ‘Everything is burnt. It is the closest thing to Hell’
• The true story of a passionate Korean 'spy'
• I shot Lennon in the back, Chapman tells parole board