By David Milliken and Kylie MacLellan
LONDON (Reuters) - The prospect of Britain leaving the European Union is a major strategic risk for Ireland, which will back attempts by Prime Minister David Cameron to reform the bloc if the terms are realistic, Ireland's leader said on Monday.
Cameron, who has promised to overhaul Britain's EU ties ahead of a referendum on a membership by the end of 2017, is due to outline his demands in a letter to the President of the European Council on Tuesday, effectively kicking off the renegotiation process.
The Times reported on Monday that Cameron favours holding the in/out vote next June if talks at a December summit go well.
"Ireland regards the prospect of the UK leaving the EU as a major strategic risk," Prime Minister Enda Kenny told a business conference in London ahead of a meeting with Cameron.
"There is a lot of goodwill to assist him in making the case for Britain in the EU," he said. "In general, where the UK seeks reasonable and achievable adjustments, we will be sympathetic and supportive."
Cameron, who has said he rules nothing out if he fails to get the changes he wants, has stepped up his case against Eurosceptics in recent weeks, stressing the benefits of being in a reformed EU.
Most opinion polls show Britons favour staying within the bloc although the gap with those wanting to leave has started to narrow.
Speaking at the same conference, Cameron said his renegotiation ultimately came down to how flexible the EU would be in accommodating the needs of both eurozone and non-eurozone countries.
"If it's flexible enough, we'll stay. If it's not flexible enough we'll have to ask ourselves a very profound question: is this organisation for us?," he said.
During his speech Cameron was heckled by two protesters who said they were able to enter the conference after Vote Leave, one of the campaign groups seeking to persuade Britons to exit the EU, secured their accreditation.
The Times, citing officials, said the vote could come as soon as June next year.
It said EU allies had been told that if a December summit of EU leaders went well, Cameron would prefer to hold the referendum in June 2016 rather than the autumn. It said he had been persuaded by other EU leaders that the vote should not be delayed, with another migration crisis likely next summer.
The British leader's office said the government had not made any decisions on the date of the vote and that it would be determined by the outcome of the negotiation.