The Kurdish, Sunni and Shiite regions would each be responsible for their own domestic laws, administration and internal security. The central government would control border defense, foreign affairs and oil revenues. Baghdad would become a federal zone, while densely populated areas of mixed populations would receive both multisectarian and international police protection.

Decentralization is hardly as radical as it may seem: the Iraqi Constitution, in fact, already provides for a federal structure and a procedure for provinces to combine into regional governments.

Besides, things are already heading toward partition: increasingly, each community supports federalism, if only as a last resort. The Sunnis, who until recently believed they would retake power in Iraq, are beginning to recognize that they won't and don't want to live in a Shiite-controlled, highly centralized state with laws enforced by sectarian militias. The Shiites know they can dominate the government, but they can't defeat a Sunni insurrection. The Kurds will not give up their 15-year-old autonomy.

Some will say moving toward strong regionalism would ignite sectarian cleansing. But that's exactly what is going on already, in ever-bigger waves. Others will argue that it would lead to partition. But a breakup is already under way. As it was in Bosnia, a strong federal system is a viable means to prevent both perils in Iraq.

The second element would be to entice the Sunnis into joining the federal system with an offer they couldn't refuse. To begin with, running their own region should be far preferable to the alternatives: being dominated by Kurds and Shiites in a central government or being the main victims of a civil war. But they also have to be given money to make their oil-poor region viable. The Constitution must be amended to guarantee Sunni areas 20 percent (approximately their proportion of the population) of all revenues.