The committee bestowed the prize for Obama's intentions, not his achievements, since nominations were closed right after he took office. Committee members wanted to build support for his efforts to promote "a new climate in international politics."

The award is an obvious rebuke to the unilateralism of the Bush presidency, and an endorsement of Obama's pledge to pursue diplomacy and dialogue and to seek a world without nuclear weapons. Nobel committee chairman Thorbjoern Jagland said the members wanted to act now to boost Obama's policies because "it could be too late to respond three years from now." But can the award really advance Obama's goals?

Nothing more clearly demonstrates the gap between Nobel hopes and on-the-ground reality than the fact that the prize was announced on a day when Obama was holding White House talks about strategy in Afghanistan.

Obama may seek dialogue, and may even encourage Afghan reconciliation with low- and mid-level Taliban. However, senior Taliban leaders and al-Qaeda aren't interested in compromises. They want to take control of Afghanistan and use it to destabilize Pakistan and get hold of that country's nuclear weapons. Nobel Prize be damned.

The peace prize may enhance Obama's appeal to rational actors in the international community who play by global rules. But the ideologues of the current Iranian regime want to play by their own rules.

Leaders who are focused on narrow national goals, such as Russia's Vladimir V. Putin, don't act like good global citizens. Any Kremlin deal on cutting nuclear weapons will be based on realpolitik, not Nobel medals.

The prize won't produce compromises between Israelis and Palestinians or Indians and Pakistanis. Nor will it overcome U.S. domestic political squabbles over the economic costs of combating global warming.

It will symbolize aspirations that Obama cannot meet for reasons that often are beyond his control, and reflect the mess he inherited from his predecessor. It will intensify the weight of global expectations on a president already overburdened.

Already, the award has sparked a round of churlish assertions from some Republicans and a few Democrats that the president didn't deserve it. (Mercifully, Sen. John McCain pointed out, with characteristic graciousness, that Americans should be proud when their president "receives an award of that prestigious category.")

No wonder senior U.S. officials were stunned by the unexpected announcement. No wonder Obama said, "This is not how I expected to wake up this morning." I'll bet he was also thinking: "Do I really need this?"

The president rightly observed that the prize was not a reward for his accomplishments, but rather "a call for all nations to confront the common challenges of the 21st century," including the twin threats of terrorism and nuclear weapons, and the dangers posed by climate change. He repeated his call for "a new era of engagement" in which all nations take responsibility for confronting these threats.

Yet the reason the Nobel committee rushed to give him a premature peace prize is the same reason his calls for engagement often ring hollow: Most nations are unwilling to engage. They don't want to take up their global responsibilities, don't want to give up their economic advantages, don't view the threats the same way.

The Norwegian Nobel committee is desperately looking to Obama because he embodies its last best hope in a world that seems condemned to continued ethnic and religious conflicts, as the global economy founders. The committee realizes the danger of a world without any superpowers, in which Russia, China, Europe, and emerging nations go their own selfish ways. It wants an American superpower to lead, but wants a leadership whose vision it admires.

This puts a huge burden on Obama: His vision requires the great powers to recognize their common interests. "He has changed the tone of U.S. foreign policy," as former Sen. Sam Nunn said, "and reshaped the global focus and debate." But will others follow his lead?

The answer will depend on Obama's strengths, about which we're still learning. At best, the prize will burnish his overseas aura and may help on the margins. At worst, it will serve as a sobering reminder that dialogue is not magic, even though it's worth trying.

So Obama was wise to downplay the prize and stress that it was awarded for a vision, not an individual. He was also wise to stress that he must focus on America's problems.

The Nobel is nice but won't help resolve his most pressing issues. Despite the good intentions of the Nobel committee, Obama must operate in the real world.