By Peter Griffiths
LONDON (Reuters) - Britain will keep its strong relationship with the United States even if it votes to leave the European Union in a planned referendum, a leading Republican senator tipped as a possible 2016 presidential contender said on Tuesday.
In a speech on Anglo-American ties in London, Marco Rubio, a first-term U.S. senator from Florida, said the United States must respect the wishes of the British electorate in any vote on its membership of the 28-nation bloc.
The comments from a politician seen as an early favorite for the Republican presidential nomination offer some support for Prime Minister David Cameron, accused by critics of risking Britain's global standing with his pledge to hold an EU vote.
"Our alliance, our partnership and our affection for your nation will continue regardless of the road you choose," Rubio said in a speech at the Chatham House think-tank.
The remarks contrast with an unusually strong warning from a senior member of Democratic President Barack Obama's administration in January that Britain must avoid "turning inwards" over Europe.
Obama told Cameron in the same month that he wanted a "strong UK in a strong EU", according to a summary of a phone call between the two released by the White House.
Cameron's promise to renegotiate the terms of Britain's EU membership before an in/out referendum by 2017 was welcomed by Eurosceptics in his ruling Conservative Party, who are trailing in the polls and face a threat at the 2015 election from the small UK Independence Party, which wants to leave the bloc.
But the pledge left him open to claims he had endangered Britain's long-term interests for short-term political gains.
Deputy Prime Minister Nick Clegg, leader of the pro-EU Liberal Democrats, who share power with the Conservatives, has said the United States would not take Britain seriously if it were "isolated and irrelevant" in Europe.
Clegg said in October the "special relationship" with the United States - a notion successive British leaders have promoted since World War Two - was based partly on Britain "being valuable to our American friends".
In a speech about the future of that relationship, Rubio said Washington needed a strong EU to help stabilize the continent and act as a global partner.
But the Cuban-American - who rose to prominence with the backing of the conservative Tea Party movement before positioning himself as an internationalist - said it was up to Britain to decide if it wanted to remain in the bloc.
"As for Britain's role in Europe, that should be a matter for the British people to decide and for your American partners to respect whatever decision you make," Rubio said.
(Additional reporting by Patricia Zengerle in Washington; Editing by Mark Heinrich)