Boris Johnson has accused Barack Obama of "hypocrisy" over his support for the UK remaining in the EU.
|the London Mayor,Boris Johnson|
The London mayor, who backs an EU exit, told the BBC's Laura Kuenssberg the Americans "wouldn't dream of sharing their sovereignty" as the UK had done.
The US President is expected to repeat his support for Britain's EU membership when he visits the UK next week.
The White House has indicated Mr Obama is ready to offer his view but will stress it is a decision for UK voters.
Backing from Mr Obama could give a boost to Prime Minister David Cameron's efforts to persuade the country to vote to stay in the EU in 23 June's referendum.
Mr Johnson said everything about the history of the US suggested they would never "share sovereignty".
Turning to the US president, he said: "I don't know what he is going to say but, if that is the American argument then it is nakedly hypocritical. The Americans would never dream of it."
He added: "I think that President Obama has got a perfect right to make any intervention that he wants. Indeed I welcome the views of everybody in this debate.
"I just find it absolutely bizarre that we are being lectured by the Americans about giving up our sovereignty and giving up control when Americans won't even sign up to the international convention on the law of the seas, let alone the international criminal court."
On Friday evening, at a rally in Manchester, Mr Johnson said leaving the EU would be a "glorious alternative" to a current system based on "the whims of unelected bureaucrats".
But speaking in Washington, Chancellor George Osborne said it was the "overwhelming view" of foreign governments and international institutions, such as the IMF and Nato, that the UK should remain.
Boris Johnson could hardly be more dismissive of the arguments being put forward by the prime minister, the IMF, the Bank of England, Nato and the White House.
The mayor of London said economic concerns about leaving the EU are fundamentally wrong and claimed the union is corrupt.
And he said that President Obama's likely warnings about departure would be nakedly hypocritical.
Remain campaign sources say those arguing to leave can't answer basic questions about the economic risks and can't attract the backing of any third parties of any stature.
When pressed for endorsements to rival the In camp, the mayor of London stumbled.
Yet Mr Johnson described his colleagues who want to stay in the union of being the Gerald Ratners of British politics. They believe the EU is "crap" - his word - but say there is no alternative.
Maybe his plain speaking is the passion of the newly converted.
But with Boris Johnson as one of the Leave campaign's biggest voices, if they lose, it won't be for fear of being bold.
On Friday, Vote Leave kicked off the first day of official campaigning on the referendum by claiming that millions saved in subscription fees to the 28 nation bloc by an exit could be spent on public services like the NHS.
However, Labour MP and Remain campaigner Chuka Umunna accused Mr Johnson of posing as a "champion of the NHS" while supporting spending cuts.
Mr Umunna said: "If we vote to leave the EU, the prime minister will almost certainly be forced out of office and most likely replaced by Boris Johnson - someone who has no love for public services and would happily watch the workers' rights people get from the EU eroded."
Pro-European Conservative MP Ken Clarke has, meanwhile, predicted Mr Cameron "won't last 30 seconds" as prime minister if the public votes to leave the EU.
He told BBC Radio 4's The World This Weekend: "We'd be plunged into a Conservative leadership crisis which is never a very edifying sight."
Mr Clarke added: "He'd be in a farcical position having campaigned for a position that's been rejected.
"He'd be a prime minister facing a Parliament in which the majority of the MPs wanted to remain in the EU."
'Uncommonly pessimistic'He said it was hard to imagine Mr Cameron could work with those who had campaigned for an exit on negotiations to negotiate a new deal for Britain in such circumstances.
Mr Johnson described Mr Clarke's argument as "uncommonly pessimistic".
He said Mr Cameron would be in a "strong position" to lead post-referendum negotiations and there were no previous examples of European leaders who had been forced to step down after suffering "adverse referendum results".
"Obviously David Cameron should remain in place," he added.