In bid for top EU job, Juncker promises fair deal for Britain

* Commission President candidate wants answer to British question

* Juncker wants 5-year freeze on new EU members

* Warns London not to block extra power for euro zone

By John O'Donnell

BRUSSELS, April 23 (Reuters) - Britain should get a fair hearing for its concerns about the European Union but must not block extra powers for the euro zone, Jean-Claude Juncker, a leading candidate to take one of the bloc's top posts, said on Wednesday.

The remarks, twinned with his pledge to halt expansion of the 28-member union for five years, offers the prospect of a face-saving compromise for British Prime Minister David Cameron should Juncker become president of the European Commission.

If Cameron is re-elected next year, he has pledged to allow Britons to vote in 2017 on whether to leave the EU.

Avoiding a split with Britain is one of the biggest challenges facing the European Union, which is preparing for European elections next month to install a new parliament and to chose some of the EU's top officials.

"I will work for a fair deal with Britain," Juncker, former prime minister of Luxembourg, told journalists in Brussels. He also advocated a five-year freeze on new members joining the EU "to keep order", a message that may soothe concerns in Britain and elsewhere about immigration from poorer eastern European countries.

But while he praised Britain's "openness", the centre-right candidate to head the powerful European Commission warned London against blocking new powers for the euro zone.

"We can formulate answers to British requests ... but ... Britain has to accept that we want to strengthen the euro zone by adding new powers, I wouldn't say to Brussels, but to the euro area," he said.

Juncker referred to his desire, for example, to establish a full-time president for countries using the currency, a step which may need British consent.

He also spoke of the difficulty of managing the 28 countries in the European Union, each with their own commissioner - a group so large that "compromises very often are taking away from the intelligence and the wisdom".

"I am of the opinion ... that there will be no new accession during the next five years," he said of accepting new members.

'LISTEN TO BRITAIN'

For decades, elections to the European Parliament have been a low-key affair, with modest turnout. That may change this year because a new EU treaty has given the parliament more say in policy and in choosing the Commission president.

Whichever political group emerges as the largest in parliament following the May 22-25 elections is expected to have first claim on the presidency post, although the choice also has to be approved by EU leaders.

Polling indicates that the centre-right parties in Europe have a narrow lead over their social democrat rivals, according to PollWatch 2014.

A new Commission president will assume office for five years from November, succeeding incumbent Jose Manuel Barroso and taking charge of an institution responsible for proposing EU law and policing existing rules. The Commission also leads trade negotiations and coordinates foreign policy.

Cameron has promised to back continued EU membership in a British referendum provided Brussels agrees to terms ranging from cutting red tape to tackling immigration.

Juncker, who played a significant role in handling Europe's debt crisis, leading the Eurogroup of euro zone finance ministers, also urged Britain to be reasonable.

"We have to listen to Britain, but Britain and the British political society has to listen to the other member states," he said. (Editing by Susan Fenton)