European fans will cheer on US presidential candidate Barack Obama as he visits Berlin, Paris and London this week, but governments wary of his inexperience and evolving policies fear the euphoria is overdone. Largely an unknown quantity in Europe, the Democratic contender is due to land in Berlin on Thursday, kicking off the second part of a foreign tour that began in the Middle East with a speech on trans-Atlantic relations in the German capital.

His appearance at the Victory Column in Berlin's central Tiergarten park is expected to draw huge crowds and is being likened in advance to former President John F. Kennedy's celebrated Ich bin ein Berliner performance of 1963.

But in the German Chancellery a few hundred metres away there is unease with the Illinois senator's cult-like following and scepticism about whether he can live up to the hype.

"There is a sort of Obama-mania in Germany right now, but I think a lot of people will have their illusions shattered if he does become President," an official in Chancellor Angela Merkel's office told Reuters, requesting anonymity.

Some European officials recalled how difficult trans-Atlantic relations were in the first few years of President Bill Clinton's administration because of his inexperience and the time it took to get his team into place.

"It is not the inexperience of Mr Obama that should concern people but more the risk of a vacuum for a while," one EU diplomat said.

But a survey released by the Pew Research Centre last week showed Germans vastly prefer Mr Obama to John McCain, his Republican challenger for the presidency, by a 49 point margin. In France it is an even wider 51 point margin and in Britain 30.

Mr Obama's vow to pull US troops out of Iraq and talk with Iran have won him admirers in Europe, particularly in Germany and France, countries that opposed the Iraq war and where President George W. Bush remains deeply unpopular because of the military adventures of his first term.