* Policy speech has been repeatedly delayed
* Address seen as fateful for British prime minister
* Politicians think it could also redefine UK's global role
* Advance excerpts reflect serious British worries about EU
By Andrew Osborn
LONDON, Jan 21 (Reuters) - British Prime Minister David Cameron will deliver a long-delayed speech on the European Union on Wednesday, stepping into a political minefield that could redefine Britain's role in the world and determine the rest of his own career.
Cameron is expected to say which powers he wants to try to claw back from the 27-nation bloc and to promise some kind of a referendum on what he calls a "new settlement" if he wins a general election in 2015.
His decision to deliver the speech on Wednesday in London so soon after it was postponed from last Friday because of the Algeria crisis is a reflection of how much pressure he is under from his own ruling Conservative party, and from nervous foreign allies, to spell out his EU vision.
Long divided over Britain's relations with Europe, the Conservatives risk losing votes to the upstart UK Independence Party which is gaining support from Britons who fear their country is increasingly dictated to by the EU.
A group of influential Conservative lawmakers want Cameron to table a straight in/out referendum on the EU, business leaders are anxious he end uncertainty on the subject, and opinion polls show public opinion towards the EU has generally soured.
Pressure to get the speech right is high. Some politicians have said it could end up reshaping Britain's role in the world, alienating allies, and deciding Cameron's own political fate and that of his ruling Conservative party.
"Wednesday morning in London fits best with the prime minister's schedule," Cameron's spokesman said of the speech, saying the premier would field his usual weekly question and answer session in parliament after the address.
"There's a debate going on across the European Union and also an active debate here in the United Kingdom and the prime minister's speech will be reflecting both of those," the spokesman said.
Some Eurosceptic MPs within his own party have framed the speech as a moment that will make or break Cameron's premiership, hinting they will stir up trouble against him if he fails to say or do enough on an issue that brought down Margaret Thatcher, one of Cameron's predecessors.
But EU states such as France have rejected the idea that Cameron will be able to plump for an "a la carte" EU, and the United States, a close ally, has said it would prefer if Britain had a strong voice within the EU.
"The anti-European people in his party want a clear message but on the other hand the EU and people in Germany expect some pro-European news from Cameron," said Stephan Mayer, a lawmaker in Germany's CSU party.
Cameron has repeatedly said he wants Britain to remain an EU member. But he has said it is right to try to renegotiate significant elements of that relationship in order to reflect closer euro zone integration and growing Euroscepticism at home.
Advance extracts of his speech released on Friday show Cameron is planning to say that Britain will drift out of the EU and that the European project will fail unless the bloc tackles three serious problems he believes it faces: the euro zone debt crisis, faltering competitiveness and declining public support, particularly in Britain.
A government source told Reuters that "four or five people" who shared "a range of views" about the EU had worked on the text.
Politicians at home and abroad have warned Cameron against pushing his country towards the EU exit and some analysts have likened his attempts to try to renegotiate Britain's membership of a club it has been in for four decades to walking through a minefield. [ID: nL6N0AL9TR]
"It's obvious that Cameron is under tremendous pressure," Katja Doerner, a German lawmaker from the opposition Greens, told Reuters.
"I think it's inopportune to intermingle the widespread and necessary criticism concerning austerity politics, the lack of democratic legitimacy etc. with Britain's renegotiation ideas," she said. "At least in Germany that kind of criticism calls for more and deeper European integration, while Cameron is arguing for less."
Cameron's decision to deliver the speech on Wednesday came as a new Guardian/ICM opinion survey showed his Conservative party was five percent behind the opposition Labour party in the polls, after three straight months in which the gap in that particular polling series had been 8 percent.