UNITED NATIONS - Some of the world's most firebrand leaders step into the global spotlight Wednesday, when the normally diplomatic, dignified corridors of the United Nations may well ring to a different tune.
Israel has already urged heads of state and their delegations taking part in the UN General Assembly to boycott a speech by Iranian leader Mahmoud Ahmadinejad for his repeated denial of the Holocaust.
And Libya's President Moamer Kadhafi, known for his long, rambling speeches on the history of the Arab people more usually delivered in his nomad tent, will step up to the UN podium for the first time in his four-decade rule.
Kadhafi, like the other heads of state and government who will address the 64th session of the 192-member body over the coming days, will find themselves limited for time.
But their words are likely to be keenly dissected as the world's top diplomats grapple for resolutions to some of today's most pressing issues, from global warming to the proliferation of nuclear arms and the financial crisis.
UN chief Ban Ki-moon will seek to set the tone by appealing in his opening address for "genuine" collective action by world leaders to roll back climate change as well as global poverty.
"If ever there were a time to act in a spirit of renewed multilateralism -- a moment to create a United Nations of genuine collective action -- it is now," Ban said in remarks prepared for delivery.
But it is likely all eyes will be on Obama, expected to renew a pledge of close partnership with the world body, in sharp contrast to his predecessor former president George W. Bush, who many felt rode roughshod over the hallowed UN halls.
Kadhafi's speech, coming just after Obama's, will also face close scrutiny with US officials hoping he will steer clear of the controversy over the release of the convicted Lockerbie bomber, in what will be a rare global address by the Libyan leader.
Presidents Luiz Inacio Lula da Silva of Brazil, who has pledged to champion the cause of emerging democracies, China's Hu Jintao and Iran's Ahmadinejad, under fire for his country's suspect nuclear program, also address the assembly Wednesday.
Israel has called for a symbolic protest against Ahmadinejad, but it was not yet clear whether many countries would comply or not.
"The simple fact of leaving the room during his speech, or not to be present during it, is a symbolic act," Israel's UN ambassador Gabriela Shalev told army radio.
"We are not trying to get promises (of a boycott) from the countries with whom we are talking. We are simply reminding them of how dangerous this person and the country that he leads are."
Iran has been rocked by its worst unrest since the 1979 Islamic revolution in the wake of its disputed elections in which Ahmadinejad was re-elected.
And the rising temperatures inside the UN headquarters may be matched by protests on the streets outside, with organizers saying thousands are set to rally against the regime "to warn against the dire implications of offering diplomatic and political incentives to the Iranian regime."
Russian President Dmitry Medvedev will also take the floor on Wednesday as the West looks to its former Cold War foe for help in both Afghanistan and in reining in Iran's nuclear ambitions.
The issue of nuclear non-proliferation, meanwhile, takes center stage on Thursday with Obama to chair an unprecedented summit in the 15-member UN Security Council.
That summit will come just a week before the five Security Council permanent members -- the United States, Russia, China, Britain and France, plus Germany -- are due to meet Iran's top nuclear negotiator Saeed Jalili on October 1.
Ahmadinejad's office has said the Iranian leader was coming to New York bearing a message of peace.
But he stirred new controversy on Tuesday when he said the people of France deserve better than their leaders, in response to similar comments by the French president after Iran's contested elections.
"The French people deserve better than their current leaders," he told France 2 television. "This Mr Sarkozy is meddling in the internal affairs of our nation. I too have a similar view," Ahmadinejad said.