NEW YORK, Sept 23, 2009 (AFP) - US President Barack Obama will get his first chance Wednesday to address the world on the ambitious sweep of his foreign policy from center stage at the UN General Assembly.

Obama will speak to heads of government and delegations in the UN chamber, and their populations beyond, in what aides are billing as a "historic" address that will lay out the "new direction" he has set for American foreign policy.

In another day on the diplomatic high wire, Obama will also meet Russia's President Dmitry Medvedev, a week after abandoning a missile shield in Eastern Europe but denying that "paranoid" objections from Moscow were the reason.

He is also due to have his first face-to-face meeting with Japan's new Prime Minister Yukio Hatoyama.

The president gave a preview of the tone of his remarks to the UN on Wednesday in an address to former president Bill Clinton's annual global forum in New York.

"Around the world, even as we pursue a new era of engagement with other nations, we are raising a broader engagement, new partnerships between societies and citizens, community organizations and businesses," he said.

"We have been speaking directly to people around the world, including our friends across the Muslim world, with whom we launch new beginnings based on mutual interests and mutual respect."

"This spirit of partnership is a defining feature of our foreign policy."

A senior Obama administration official said the president would discuss how America was responding "aggressively" to global challenges and call on other nations to live up to their responsibility to act.

"He will detail the priorities of non-proliferation, peace and security, climate change, and global growth and development, and underscore America's fundamental commitment to universal values -- and challenge others in the United Nations to do the same," the official said.

The new US president's appearance at the UN offers other world leaders a chance to size up his diplomatic leverage, as a long list of testing domestic and foreign policy challenges bear down on the White House.

He got his first look at the view from the podium in the UN chamber on Tuesday, as he delivered a major speech on global warming, saying the United States was "determined" to carve out a new leadership role on climate change.

But Obama's hope for international cooperation is already being sorely tested, with wide divisions evident on issues that include the fight against climate change and whether to impose more punitive sanctions on Iran over its nuclear program.

Obama's speech will be closely watched to see if Iran's firebrand President Mahmoud Ahmadinejad is on the floor of the UN chamber, and for his reaction.

Iran has so far refused to accept Obama's call for direct dialogue and the showdown over the Islamic Republic's nuclear program will hit a pivotal point when it sends officials to talks with world powers on October 1 in Geneva.

The president also got a taste of the frustrations of mediating the intractable Middle East conflict on Tuesday, when he was unable to get Israeli and Palestinian leaders to agree to open talks, after a three-way summit.

Obama's UN address comes amid an exacting week on the world stage. On Thursday he moves on to Pittsburgh to cajole fellow world leaders to agree to recession exit strategies at the G20 economic summit.

When Obama strode on to the world stage in April, at the last G20 summit in London, he was still surfing the euphoria of his historic inauguration, with domestic approval ratings above 60 percent.

Things are somewhat different as he steps to the podium on Wednesday.

With his popularity pummeled by the battle over his landmark health care reform drive, Obama is clinging to majority approval in most polls.

Many of Obama's top priorities -- including climate change legislation and financial regulatory reform on which G20 partners are demanding action -- are facing heavy weather in Congress.

Obama aides argue that he has transformed the image of the United States abroad following the transatlantic schisms of George W. Bush's presidency, a view backed up by recent polling.

But there is little evidence so far that he has changed the paradigm of festering global conflicts.