* Cameron says in-out referendum soon a "false choice"
* He is expected to give major EU speech next week
* Says optimistic about redefining EU-UK relationship
By Mohammed Abbas and Andrew Osborn
LONDON, Jan 14 (Reuters) - British Prime Minister David Cameron on Monday played down the prospect of a referendum any time soon on whether Britain should leave the European Union, defying calls from within his Conservative Party and the public.
Cameron is expected to explain how he wants to change Britain's relationship with the EU next week, in a speech that could set a course for leaving the 27-member bloc, deepen fractures within his own party, and strain ties with his Liberal Democrat coalition partners.
A weekend poll by influential website ConservativeHome found that 78 percent of Conservative Party members either want Britain's relationship with the EU reduced to access to its common market or to leave the bloc altogether.
"If we had an in-out referendum tomorrow, or very shortly, I don't think that would be the right answer for the simple reason that I think we would be giving people a false choice," Cameron told BBC radio.
"Right now I think there are a lot of people who say 'I would like to be in Europe, but I'm not happy with every aspect of the relationship, so I want it changed'. That is my view."
Conservative infighting over Europe helped topple previous party leaders, and splits on the issue appear to be deepening as Cameron's speech nears. Media reports say he will speak on Jan. 22 or 23 in Germany or in the Netherlands.
Cameron's office declined to confirm the reports.
Communities Secretary Eric Pickles, a Conservative, said on Sunday he hoped it was in Britain's interest to stay in the EU, but "we shouldn't stay at any price".
Both pro and anti-Europe senior politicians stepped up their campaigns over the weekend, with eurosceptic Conservative group "Fresh Start" pledging to demand a radical repatriation of powers from Brussels this week.
On the other side of the debate, Conservative Party grandee Michael Heseltine said on Saturday Cameron's plan to change Britain's relationship with the EU was an "unnecessary gamble", and put the country's status as a business destination at risk.
The Lib Dems, the Conservatives' junior partners in coalition rule, are pro-Europe, and divisions over the issue threaten to put renewed strain on the partnership.
Cameron says he wants Britain to remain in the EU - a major trading partner - but is under pressure from an increasingly eurosceptic public to repatriate powers from Brussels or leave the bloc altogether.
The anti-Europe UK Independence Party has surged in popularity in the last year, wooing Conservative voters and threatening to split the right-wing vote ahead of a 2015 general election. An opinion poll on Sunday put UKIP ahead of the Conservatives in next year's European Parliament elections.
Cameron says he plans to renegotiate Britain's ties with the EU and seek the public's "fresh consent" for the new deal, telling the BBC he believed he had allies in his efforts to repatriate powers from Brussels.
He would not be drawn on how he would seek the public's approval for a prospective new deal, saying only he was "not against" referendums, though experts expect a promise of some form of vote after the 2015 national ballot.
"I'm optimistic and confident that we can achieve changes in the European Union to make sure that Britain feels more comfortable with our relationship with Europe," he said.
Cameron's official spokesman said on Monday the prime minister had "friendly and constructive" talks with German Chancellor Angela Merkel and Dutch Prime Minister Mark Rutte over the weekend on Britain's approach to the EU.
However, Cameron's speech may have already upset European colleagues before he has spoken a word, with the Financial Times reporting that the date of the address may move to Jan. 23 to avoid clashing with the 50th anniversary celebration of the Elysee treaty on Jan. 22, a significant date for Germany and France.
Foreign powers have weighed in on the debate in recent days, with the United States last week making it clear it wanted Britain to remain a "strong voice" inside the EU.
However, influential former U.S. ambassador to the United Nations John Bolton - an ally of Conservative eurosceptics - urged Britain to re-evaluate its approach to a "sclerotic" EU.
"Re-evaluating Britain's approach toward the listing EU ship is entirely sensible .... It is simply wrong for Washington to say that Britain has no choice but to accept the EU as is," he wrote in an opinion piece in the Times newspaper.