U.N. struggles to prove its relevance

She highlighted U.S. initiatives to impose U.N. sanctions on North Korea and Iran. She said the United Nations was providing a critical role in managing peace efforts in places including Sudan and supporting U.S. efforts in Afghanistan and Iraq. And she noted the United Nations's vital role in responding to natural disasters in places such as Haiti and Pakistan.

"We've seen tangible results that in fact will make Americans safer and make the world a more peaceful and prosperous place," she said. "We've ended needless U.S. isolation on a range of issues."

Still, during the past two years, the U.N. Security Council has made fewer decisions than at any time since the end of the Cold War, according to a report by the Security Council Report, an independent, nonprofit group.

U.N. peacekeeping, which grew rapidly during the Bush administration, has stalled. Not a single new U.N. peacekeeping mission has been authorized since Obama came into office, though the council has authorized additional troops to ensure order in Haiti after the January earthquake.

The United States and its European allies, meanwhile, have opposed calls by African governments to send the United Nations back into Somalia. And the council mounted a largely anemic effort to prevent mass atrocities of civilians in Sri Lanka. Russia, meanwhile, blocked any discussion of a peacekeeping force for Kyrgyzstan to halt violence against ethnic Uzbeks earlier this year. In Congo, the United Nations has admitted failing to provide adequate protections for victims of mass rape.

"The feeling that I get watching the [Obama] administration is that their heart is certainly there," said John Ruggie, a professor at Harvard's John F. Kennedy School of Government and an adviser to Ban. "The willingness to be supportive is certainly there, but with so many other issues to juggle and deal with I don't think [the U.N.] has become a real focus of attention."

In perhaps its most important challenge at the moment, the United Nations is leading the effort to oversee a referendum on independence for southern Sudan - a ballot that threatens to reignite one of Africa's bloodiest civil wars if it's not seen as credible.

In a bid to bolster the U.N. effort, Obama will participate in a high-level meeting this week to prod Sudan's rival camps to commit to a peaceful vote.

Edward Luck, a historian at the International Peace Institute who acts as an informal adviser to Ban, said the U.N. effort to find its way has been complicated by a "geopolitical strategic situation that is very, very murky."

"The U.N. reflects that," he said. "The world is muddling through as the U.N. is muddling through."

Luck said that situation will only become more difficult in the coming year as key emerging powers - including Brazil, India, South Africa, Turkey and Nigeria - get their turns as members on the Security Council for two-year terms. Brazil and Turkey, who are also serving, have used their position to challenge the existing order on the council, mounting a campaign, for instance, to thwart the U.S. push for sanctions on Iran.

But Luck said he was confident that the United Nations would remain a key player, noting that there are no other international institutions with the capacity to implement their policies on the ground or with the same kind of political legitimacy that comes with being an organization with universal membership.

"The U.N. is not the sun of the international solar system; everything doesn't revolve around it," he said. "But it is the final reference point on most issues, which have to come to the U.N. for legitimacy."