For the United Nations, relevance may be almost as perilous as irrelevance. In the span of a year, the Bush administration went from taunting the world body to begging for its help. A beefed-up U.N. team will soon arrive in Baghdad to advise the Iraqi government on reconstruction, social services, and human rights and directly assist with elections. At the same time, U.N. peacekeeping missions are sprouting or expanding in Burundi, Democratic Republic of the Congo, Haiti, and Ivory Coast. Indeed, by the end of 2004, more blue helmets will likely be in action than at any time in history.

Although some U.N. backers revel in the growing global reliance on the world body, now is no time to get smug. These weighty responsibilities are landing on the shoulders of an organization that national governments have deliberately kept weak. The United Nations’ 60-year-old machinery has never seemed so ill-equipped for its work, and its credibility has plummeted. As the major powers fight terrorism and dwell on homeland security, they will hand the United Nations essential but thankless tasks they might once have tackled themselves (or just ignored). Without major changes, the United Nations may well buckle under the growing strain.

The idea that the United Nations can stumble along in its atrophied condition has powerful appeal in capitals around the world—and even in some offices at U.N. headquarters. But believing that the status quo will suffice is dangerous.

Regrettably, most of those who could change the organization have an interest in resisting reform. None of the permanent Security Council members wants to give up its veto; smaller powers delight in their General Assembly votes, which count as much as those of the major powers; repressive regimes cherish participation in United Nations’ human rights bodies, where they can scuttle embarrassing...