The German Chancellor said: "Germany, and I personally, want Britain to be an important part and an active member of the European Union.
"We are prepared to talk about British wishes but we have to always keep in mind that other countries have different wishes and we have to find a fair compromise.
"We will talk intensively with Britain about its individual ideas but there will be time for that over the months to come."
However, Guido Westerwelle, Germany's Foreign Minister, was more critical, saying: "Not everything has to be decided in Brussels and by Brussels but a politics of cherry-picking will simply not work.
"Europe is not a sum of national interests but a community of fate in difficult times."
In France, Laurent Fabius, the left-wing foreign minister, was more hostile, claiming the British wrongly believed they could choose from an "a la carte" menu as EU members when everyone else had the set menu.
He also used another analogy, saying: "We are like a football club and, if you want to join the football club, you can't then say you want to play rugby."
Mr Fabius also warned the UK would find life difficult outside the EU.
Meanwhile, Guy Verhofstadt, the former Belgian premier and Liberal Democrat leader in the European Parliament, accused the Prime Minister of "playing with fire" over EU membership and warned against trying "hold the EU to ransom".
He said: "By holding out the prospect of renegotiating the terms of Britain's membership of the EU and subjecting it to a referendum, David Cameron is playing with fire.
"He can control neither the timing nor the outcome of the negotiations and in so doing is raising false expectations that can never be met."
He added: "Mr Cameron will not succeed if he attempts to hold his European partners to ransom."
Martin Schulz, the German Socialist leader in the European Parliament, accused the Prime Minister of "playing a dangerous game for tactical, domestic reasons". He warned any attempt to repatriate powers to would probably be "a drawn-out and cumbersome negotiation".
The White House welcomed Mr Cameron's "call to remain in the EU", saying it believed the UK was stronger as a result of its EU membership.