Last week's Group of Eight summit highlighted the irrelevance of some of the world's most important institutions. Atop the G8 agenda were climate change, fuel prices and the global food crisis. And yet China and India — the world's two most populous countries, second- and sixth-largest energy consumers, and second- and fourth-biggest carbon emitters — are not members of the club.

Since the fall of the Berlin Wall, globalization has transformed world politics. New power centers like China, India and Brazil have emerged. Terrorism and global warming are security concerns.

These tectonic shifts are straining the foundations of governance laid after World War II. Yet there has been no "act of creation" comparable to the late 1940s, when U.S. statesmen led the building of new global institutions. The world makes do with creaky bodies like the G8, United Nations, IMF and NATO, whose agendas reflect a world that no longer exists.

Today's global architecture should reflect contemporary power realities, threats and sensibilities. But absent another world war to clean the slate, vested interests will resist fundamental change. Unless the United States takes the lead, the reform agenda will go nowhere.

As the Bush administration straggles to the finish line, some of the most creative thinking about world order is occurring across the Atlantic. UK Prime Minister Gordon Brown has proposed an overhaul of international institutions. It is time for the two U.S. presidential candidates to engage this debate.

John McCain and Barack Obama both promise a "kinder, gentler" foreign policy. Beyond this shift in tone, their blueprints for world order are vague. We need some straight talk about which international institutions are worth preserving, which can be salvaged, and which need to be demolished. Here are several questions they need to answer:

The G8. Any global steering committee that includes Canada (population 33 million, GDP $1.4 trillion) and Italy (58 million, $2.07 trillion) but excludes China (1.33 billion, $3.25 trillion) and India (1.15 billion, $1.15 trillion) is obsolete. McCain would keep the G8 a democratic club by ejecting Russia, adding India and Brazil, and excluding China. Where does Obama stand?

The Security Council. In 2004, George W. Bush invoked John Kerry's notion of a "global test" as a cudgel to beat the Democratic nominee. And yet Iraq shows that acting without the U.N. Security Council's blessing carries steep diplomatic, military and financial costs. Under what conditions would either candidate seek U.N. authorization to use armed force? And how would they overhaul the council's membership to reflect the power shifts since 1945?

NATO. The trans-Atlantic alliance celebrates its 60th birthday next April in a mid-life crisis, divided over its mission in Afghanistan, its posture toward Russia and its relations with the European Union. How do the candidates plan to make NATO relevant to today's threats?

A Concert of Democracies? McCain advocates a league of democratic states to compete with the United Nations. Two senior Obama advisers, Tony Lake and Ivo Daalder, agree. Does Obama believe such a league would advance American global leadership — or merely complicate it?

Climate Change. Both candidates endorse a "cap and trade" system to reduce U.S. emissions. But avoiding global catastrophe will require a successor to the Kyoto Protocol at the 2009 Copenhagen Summit and cooperation among a narrower coalition of major emitters. How do the candidates propose to strike such multilateral bargains?

Global Finance. The Bretton Woods institutions — the IMF and World Bank — risk irrelevance in an era of massive private capital flows, sovereign wealth funds and rapid economic growth in the developing world. How do McCain and Obama intend to update their structures to the 21st century?

Prix fixe or a la carte? Finally, the candidates need to explain what form of multilateral cooperation they will pursue. Historically, Democrats have favored formal, universal institutions that provide international legitimacy, predictable burden sharing, and standing capabilities. Republicans have inclined toward flexible, ad hoc arrangements that protect U.S. sovereignty, restrict membership to like-minded countries, and permit decisive action.

Many around the world yearn for regime change in Washington. Whether it is change that they — and we — can believe in depends on whether the winning candidate has a meaningful agenda for global reform.

Stewart Patrick is director of the Council on Foreign Relations Program on Global Governance. He wrote this commentary for McClatchy-Tribune News Service.