BRUSSELS — British Prime Minister David Cameron appeared on Thursday to be nearing a deal with his fellow European Union leaders that could set the tone for what is expected to be a bruising campaign to decide whether the U.K. jettisons the 28-member bloc.

Meeting in Brussels, the leaders were expected to negotiate late into the night – and perhaps into Friday morning – as Cameron sought concessions that would help him make the case back home for his country’s continued membership. “I’ll be battling for Britain. If we can get a good deal, I’ll take that deal. But I will not take a deal that doesn’t meet what we need,” Cameron told reporters before the talks kicked off.

But even as the leaders haggled, analysts said the prime minister would need to settle for an agreement that falls well short of his original intention to fundamentally renegotiate Britain’s relationship with the E.U. “What he will get is not revolutionary,” said Janis Emmanouilidis, director of studies at the Brussels-based European Policy Center. “This won’t change Europe.”

A British exit, however, very much would. The country has long been an ambivalent E.U. member, but it remains one of the bloc’s cornerstones. If the country votes to leave in a referendum expected in June, it could trigger a broader European unraveling at a time when continental unity is being strained by a refugee crisis, renewed Russian aggression, terrorist attacks and rising nationalism. If Britain votes to leave, Emmanouilidis said, it would likely embolden “anti-E.U. voices in other member states saying there is a way out.”

European leaders appeared mindful of that risk as they gathered Thursday, suggesting they intended to give Cameron enough of what he wants that he’ll be able to declare victory by the time the summit ends on Friday.

“I’m going into this debate with the position that we would like to do everything to create the conditions so that Great Britain can remain part of the European Union,” said German Chancellor Angela Merkel as she arrived for the talks.