IRAQIS HAVE given the world another inspiring demonstration of their willingness to risk their lives to vote on the future of their country. Some 10 million people reportedly participated in Saturday's referendum on a new constitution, significantly more than voted in last January's elections. Though turnout was uneven, large numbers of Sunni voters chose to join the political process for the first time -- a hopeful sign that the community that harbors the Iraqi insurgency may eventually choose democracy over armed struggle. The success of U.S. and Iraqi troops in securing the polling places and preventing major attacks amounted to a significant military victory and should encourage still more voters in the next round of elections.

The results of the referendum nevertheless vividly demonstrated the political gulf that Iraqis must bridge in the coming months if they are to avoid partition and civil war. Officials said yesterday that the constitution appeared to have been ratified, though official results were not available. More significant than approval of a document already stripped of much of its substance, however, was the demonstration of mass opinion among Iraq's various communities -- in the case of minority Sunnis, the first since the fall of Saddam Hussein. While 97 percent of voters reportedly favored the constitution in Shiite Basra and 98 percent voted yes in the Kurdish province of Sulaimaniyah, 97 percent of the approximately 100,000 Sunni voters in the city of Fallujah were opposed. Two Sunni-dominated provinces where the insurgency is strongest rejected the constitution overwhelmingly, yet must now, in theory, be governed by it. In practice, this won't work: Unless more Sunni support can be obtained for the emerging political system, it won't take hold, no matter how many elections occur.

The Bush administration sometimes appears to understand this problem. It is certainly the case that its ambassador in Baghdad, Zalmay Khalilzad, has been working as hard, or harder, than any Iraqi politician to forge an agreement among Sunnis, Shiites and Kurds. Yet at other times President Bush and his senior aides publicly praise and defend the extreme form of "federalism" written into the constitution by Shiites and Kurds -- even though it is that agenda that fuels Sunni opposition and threatens to tear the country apart. Mr. Khalilzad succeeded last week in persuading the Shiites and Kurds to agree on the formation of a committee with Sunnis to discuss constitutional changes next year. But he apparently has made no headway on the underlying issues.

That means the crucial political challenges of the coming two months will be ensuring security and the fullest possible participation in scheduled parliamentary elections on Dec. 15 and drawing Shiite and Kurdish leaders back from the precipice to which they have led the country. Sunni leaders must be urged to set aside disappointment over their failure to defeat the constitution and begin their parliamentary campaigns. It will help if any irregularities or charges of fraud in Saturday's vote are vigorously investigated, and a strong international monitoring operation is established for the December vote. The United States, meanwhile, must make clear to Shiite and Kurdish leaders, and to Iraqis as a whole, that it will not support the de facto partition of the country or sacrifice U.S. lives to defend ministates created along ethnic and religious lines. Any notion that such a division of Iraq could be made to work ought to have been settled by Saturday's vote: The overwhelming majority of Iraqi Sunnis have sent the message that it is unacceptable.