By Elizabeth Piper and Robin Emmott
BRUSSELS (Reuters) - Prime Minister David Cameron took the floor at a European Union summit on Thursday to try to persuade fellow leaders to give Britain improved membership terms, including disputed relief from immigration, before it votes on staying in the bloc.
EU officials said Cameron began his pitch after European Council President Donald Tusk told the summit there was good progress on three of London's four key demands, but the fourth - to deny EU migrants in-work benefits for four years - was "very difficult".
Other leaders around the dinner table want to help Cameron ensure Britain chooses to stay in the EU in a referendum due within two years, with opinion polls showing the number of Britons wishing to leave is growing.
But the Conservative leader faced an uphill struggle to win agreement on curbing welfare payments to EU migrants to try to reduce immigration, a proposal several leaders, especially from eastern Europe, say breaks the fundamental EU principles.
"Tonight, here in Brussels, we are going to have a conversation dedicated to Britain's renegotiation of its position in Europe and I want to see real progress in all of the four areas that I have mentioned," he told reporters on arrival, referring to four topics on which he wants to negotiate change.
"We're not pushing for a deal tonight but we're pushing for real momentum so that we can get this deal done. So I will be battling for Britain right through the night and I think we'll be getting a good deal."
Over filet of venison with parsnip mousse and Szechuan pepper jus, the British prime minister sought to convince fellow leaders that the continued membership of Europe's second biggest economy and one of its two top military powers hinges on finding a convincing solution to the sensitive immigration question.
Cameron says he wants Britain to stay in the EU, but has hinted he could campaign for an exit if he fails to win an agreement that can reduce the influx of EU migrants, improve business competitiveness, give more sovereignty back to Britain and protect London's banks from discrimination by the euro zone.
His proposal to make immigrants from the other 27 EU states wait four years before claiming "in-work" benefits in Britain - income supplements to people in lower paid jobs - has been roundly criticised, especially in eastern Europe, for breaking EU law banning discrimination.
An EU aide said Tusk wanted to give everyone a chance to speak their mind on Thursday night with a view to seeking a deal at the next summit in mid-February.
Poland, Hungary, Slovakia and the Czech Republic, known as the Visegrad Group, said in a statement they would reject any British demand to change EU laws that would mean discrimination against their citizens or limit their freedom of movement.
For many Europeans born behind the Iron Curtain, that freedom is a touchstone of their post-Cold War liberation.
A British official said Cameron was offering no alternatives to his four-year proposal at the summit, but the prime minister was eager to hear whether other leaders had other suggestions that would help control immigration to Britain better.
An EU diplomat said Cameron sat in silence for more than three hours while other EU leaders debated how to deal with a wave of migrants that has divided European governments. Britain has refused to take in any from Europe.
POSITIVE NOISES
Drawing the European Union's focus to a small part of Britain's welfare system has raised eyebrows among some leaders who are trying to hammer out a deal to house the hundreds of thousands of refugees and respond to a war in Syria.
But EU officials said most were keen to help Cameron return to Britain with a message that he is winning in the talks, to turn the tide of opinion polls which suggest that those wanting to leave the bloc were gaining ground.
"There's a certain orchestration to make sure that tonight things work out well for David Cameron, to make it look as that he is winning, because no one wants a Brexit," a senior official close to the talks said.
Despite the goodwill, the difficulties of securing any agreement on welfare looked a way off.
German Chancellor Angela Merkel said she expected EU leaders to have an open discussion, but "at the same time do not want to limit the basic liberties, non-discrimination, free movement, of the European Union".
French President Francois Hollande agreed, saying it would "not be acceptable to revise the very foundations of European commitments", while a source close to the talks put it bluntly: "There's going to have to be a lot of creative thinking."
Some governments, notably euro zone powerhouse Germany, are also uncomfortable with Cameron's demand for Britain to be safeguarded from any move by the 19 countries that share the euro currency to impose rules by majority vote on the City.
Cameron has been touring capitals to drum up support for demands that he says will soothe British fears over the EU and help convince people to stay in the bloc. A British government official said he would hold bilateral talks with his Lithuanian and Greek counterparts before the dinner.
The British government hoped the dinner would signal a political will to accelerate technical talks on how London's demands can be made watertight in EU law to try to reach agreement in February.
An agreement early next year could give Cameron enough time to stage the referendum in June, seen by some analysts as an advantageous time before summer.
That is when migrants fleeing conflict and poverty in Africa and the Middle East may start making the treacherous journey to Europe, images that have fuelled fears about rising immigration in Britain -- even though Britain is not part of Europe's open-border Schengen zone, through which migrants have been moving.
"The aim will be to have this substantive political discussion on Thursday evening, looking at the progress made so far and in particular looking at some of the more difficult and trickier areas to resolve," the British official said.
(Additional reporting by Gabriela Baczynska, Alastair Macdonald, Robert-Jan Bartunek, Philip Blenkinsop, Elizabeth Pineau and Andreas Rinke in Brussels; Editing by Alastair Macdonald and Paul Taylor)
