The new United States administration assuming office next January will confront a congested menu of domestic and foreign policy items demanding immediate attention. It will need to separate the urgent from the merely important, and will be fortunate if the Bush Administration has left behind just unfinished business instead of a full-blown crisis or two.

The list of critical areas and issues is long: Iraq, the Israeli-Palestinian conflict, Afghanistan, Pakistan, Iran, and North Korea; terrorism, nuclear proliferation, human-rights abuses and atrocities, global trade, climate change, pandemics, and poverty. There are also the perennial issues such as managing the China-US relationship as a partnership or rivalry, reassuring traditional allies such as Japan and Australia, dealing with a prickly and newly assertive Russia, responding to requests for NATO membership from Georgia and Ukraine, and massaging the trans-Atlantic alliance. And then there are the unexpected problems, such as trying to coax or coerce the military junta in Burma to let urgently needed relief into the country.

How will the different candidates respond to this agenda? The discussion can be framed with respect to four critical themes: the use of force; peace operations; nuclear weapons; and climate change. Although not exhaustive, the list is representative.

Of the the two candidates (Hillary Clinton being most unlikely to win the Democratic nomination), Barack Obama is the most likely to win instant international attention, admiration and respect for the US. His persona was formed in part in Indonesia, where he learnt the triple lesson of the powerlessness and helplessness of citizens in developing countries, the status of Americans abroad, and the extent to which others look to the US to help them overcome their own political and economic problems. Obama says the US mission ''is to provide global leadership grounded in the understanding that the world shares a common security and a common humanity''.

He is the most likely to engage with the rest of the world on climate change, calling on Al Gore's assistance, and by instinct should be the most responsive to providing US logistical and political support for United Nations peace operations in Africa. He is also the only one to have shown interest in pursuing the goal of a nuclear-weapon-free world while downgrading its role in the interim and ratifying the Comprehensive Test Ban Treaty.

As for the use of force, he has been the most circumspect of the three candidates, for example, with Iraq and Iran. He has shown the clearest understanding of the broader damage done to US interests and leadership by the distraction in Iraq and promised to bring it to ''a responsible end''. Yet he also said that he would not hesitate to take military action inside Pakistan, even without its permission, if there was actionable intelligence to indicate the presence of high-value terrorist leaders there.

Overall, nonetheless, he is likely to strive to ''harness American power to reinvigorate American diplomacy''. His understanding of the reforms needed in the UN system are not substantially different from the Bush Administration's.

John McCain is the only one of the three to know first-hand what war means. The misrepresentations of his ''100 years in Iraq'' comment notwithstanding, therefore, he could be more cautious than Clinton but because of his party less restrained than Obama in defending US interests with force. He has based his campaign on winning the war in Iraq and not losing focus from the war on terrorism. He seems more interested in cooperating with a coalition or league of democracies than giving priority to the UN.

Based on that, like Bush he would most likely differentiate between US-friendly and US-hostile regimes possessing or pursuing nuclear weapons, enlisting the former as strategic partners and allies while sanctioning the latter as threats to world peace. But he could also offer Reaganesque surprises if the idea of a nuclear-weapon-free world propounded by four former Republican heavyweights grabs his attention. Neither by personal instinct nor by party leanings is McCain likely to pursue an activist agenda with UN peace operations and climate change. As he is the least likely of the three to serve for a second term (based simply on age), he may have the least longer-term impact.

Regardless of who becomes president, to regain its former status as a good international citizen, the US should reinvest diplomatic assets in the UN, regain its former role as the champion-in-chief of the global human-rights norm, ''re-sign'' and ratify the Rome Statute of the International Criminal Court that was ''unsigned'' by Bush in 2002, reaffirm firm adherence to the Geneva and UN torture conventions, ratify the Comprehensive Test Ban Treaty, and assume the leadership role in negotiating a post-Kyoto climate deal.

What of the relationship with the UN? The US is neither a humble nor a dispensable power. Nor is the UN a disposable organisation, even for the most powerful nation in history. It remains an unsubstitutable forum and an indispensable font of authority for reducing the transaction costs of US diplomatic engagement with the rest of the world. The new administration will have to pay early attention to repairing and revitalising the relationship with the UN that has been strained and frayed.

In Afghanistan, the two are already working together closely and have done so from the start. This is one reason why the US role in Afghanistan remains relatively uncontroversial.

In Iraq, for US troops simply to withdraw would create a dangerous vacuum. Only the UN has the legitimacy to authorise a replacement multinational presence for stabilising security and the capacity to mobilise the requisite resources for post-conflict reconstruction in Iraq.

The opinions expressed in this article/multimedia are those of the author(s) and do not necessarily reflect the views of CIGI or its Board of Directors.