AMID ALL THE bad news from Iraq this week, it has been somewhat encouraging to hear the hints from several Iraqi political leaders, as well as from U.S. Ambassador Zalmay Khalilzad, that the Iraqi constitution may still be open to modification before it is put to a vote in an October referendum. That is promising not only because of the possibility that near-total Sunni opposition to the charter could be fractured by further negotiation and compromise. It's important also because the United States has a strong interest in preventing the extreme form of "federalism" proposed for southern Iraq by Shiite leaders. As it now stands, senior Shiites say they favor a nine-province ministate, an entity that very well could emerge as a cleric-dominated client of Iran. The danger is that the multiethnic and democratic Iraq the United States is fighting for would not survive the birth of such a statelet and that Americans would not support its military defense by U.S. troops.

The Bush administration nevertheless has yet to decisively oppose the Shiite project, at least in public. Mr. Bush last week phoned the cleric who first announced the nine-province plan, Abdul Aziz Hakim; his party later agreed to remove some of the language spelling out the powers of the "regional" governments from the constitutional draft. The provisions now are to be legislated by the new parliament that would be elected in December if the constitution is ratified. Yet with support from Kurds, who plan to form their own ministate, Shiites would seem to be well within reach of the legislative majority necessary to impose the far-reaching provisions in the constitution's previous drafts. These would allow a Shiite region to write its own constitution, set up its own judiciary and have exclusive control over security forces and "regional guards," which presumably would be the Iranian-trained militia forces already operating in southern Iraq. The Shiite-Kurd plan provides that in all cases where federal and regional laws conflict, the regional will take precedence.

Some form of federalism is necessary in Iraq, and most political leaders long ago accepted that the minority Kurds, a non-Arab people who have enjoyed de facto autonomy since 1991, would preserve that status. But the Shiites are not a minority: By the most common estimate, they make up 60 percent of Iraq's population. No democratic national government will be able to persecute Shiite-populated regions or deprive them of resources, as did Saddam Hussein. In a united and pluralist Iraq, however, other groups will act as a necessary check on radical Shiite tendencies. If the national constitution had been the exclusive work of Shiite leaders, for example, Islam would have been made the sole source of law and all social affairs would have been governed by clerical courts using sharia law. As it stands, the charter is among the most liberal in the Muslim world, though the implementation of many key provisions will depend on the future balance of power in parliament. Similarly, Iran could never make a multiethnic Iraq into a satellite, but a Shiite ministate could easily fall under Tehran's influence, even if the top Iraqi Shiite leaders were not -- as most are -- longtime allies.

Some Sunni leaders and the Sunni insurgency will go on opposing the constitution regardless of its terms. Their ambition is to restore Saddam Hussein's Baathist dictatorship. But the United States could raise the chances of winning support from moderate Sunnis, and better protect its own vital interests, by insisting that Mr. Hakim and other leaders abandon, or drastically scale back, any plan for a Shiite-dominated region. At least for now, the Shiite political movements in Iraq cannot achieve even their legitimate aims without the support of the U.S. military. If more Americans are to give their lives for Iraq, Mr. Bush should make clear that it can only be for a country that is federal but united.