UNITED NATIONS - President Obama will travel this week to New York for the annual U.N. gathering of world leaders to reaffirm America's commitment to a "new era of multilateralism." He will arrive, however, at a time when the United Nations, the world's principal multilateral institution, is struggling to remain relevant on the world stage.

From nuclear diplomacy with North Korea to economic negotiations among the Group of 20 nations and peace talks in the Middle East, U.N. diplomats have frequently been reduced to bit players over the past year.

Even on climate change, an issue on which the United Nations has tried to stake its claim, the world body has failed to show much progress. Highly anticipated negotiations in Copenhagen ran aground in December.

For an institution with its share of proud chapters, these are tough times.

"A lot of the juice is outside the United Nations," said Bruce Jones, the director of the Center on International Cooperation at New York University. "The old days when the U.S. and the Europeans could stitch things up at the United Nations are over, and we haven't yet seen the emergence of a new platform for action or a consortium for action at the U.N."

Jones noted that the growing assertiveness of emerging powers - particularly China - has made it harder to reach international compromise. But the United Nations has been hobbled by failures, and distractions, of its own making.

The outgoing head of an anti-corruption office delivered a parting shot to Secretary General Ban Ki-moon in July, accusing him of leading the United Nations into an era of decline. More recently, the top Chinese official at the United Nations, in an alcohol-fueled outburst, noted at a U.N. retreat that he had never really liked Americans, or his boss, Ban.

Asked to comment about the Chinese diplomat at a recent press briefing, the secretary general sighed and urged reporters to turn their attention to more pressing international problems.

The U.N. General Assembly, the world's biggest international diplomatic debate, still provides an opportunity to take stock of America's role in the world, as well as a platform for authoritarian leaders to air their grievances. During the past decade, the General Assembly chamber has reflected the strains of global policymaking, with President George W. Bush lecturing the world body about its failure to confront Saddam Hussein and Venezuelan President Hugo Chavez famously comparing Bush to the devil.

This year, the mood is favorable for an American president who has restored U.S. funding to the United Nations, ended a U.S. boycott of the U.N. Human Rights Council, and reinvigorated U.N. nuclear disarmament efforts.

On Wednesday, Obama will also reaffirm U.S. support for a series of U.N. development targets, known as the Millennium Development Goals, before the General Assembly begins in earnest.

The Obama administration, however, will make no new financial pledges to the campaign.