Sunni, Shiite and Kurdish negotiators in Iraq are scrambling to reach an accord on a new constitution. Iraq's Parliament is scheduled to vote on the charter Thursday. But the Sunnis reject the concept of federalism that is at the core of the draft constitution and may be looking ahead to a planned referendum in October as a chance to block the document.

Iraqi lawmakers listen to parliament speaker Hajim al-Hassani in Baghdad, Monday, Aug. 22, 2005

Monday night, the speaker of parliament, Hajim al-Hassani, announced three more days of discussions to try to reach consensus on the constitution. But the one thing that Sunni, Shiite and Kurdish leaders seemed to agree on by Tuesday, was that they would need more than three days to work out their differences.

While the Shiite and Kurdish blocs managed to hammer out a last-minute agreement between themselves, this left major differences with the Sunni Arabs, who cling to the idea of a centralized state despite Shiite demands for fiscal and administrative autonomy in the oil rich south.

The most outspoken of the Sunni negotiators, Salih al-Mutlaq, said the Shiites and Kurds had submitted the draft to parliament illegally - since it was supposed to be based on a consensus from all committee members.

"First, because we agreed with the national assembly that all decisions would be taken through consensus," he said. "And we told them, at the last minute, that we don't agree about this constitution. And they passed it."

Despite some initial hints of doubt, Kurdish leaders stood behind the proposed text, apparently satisfied that it would preserve their self-rule in the north, and would not trample on basic freedoms in the name of applying Islamic law.

The proposed constitution defines Iraq as a "federal state," and as part of the "Islamic," rather than "Arab" world.

Sunni politicians at first called the draft a provocation, warning of even more sectarian violence as a result. But they are also looking ahead to the constitutional referendum scheduled for October 15. With their geographic concentration in the west and northwest of Iraq, Sunni Arabs could still block the proposed constitution then.

Two-thirds of voters in any three of Iraq's 18 provinces would be sufficient to reject the proposed constitution, sending the whole drafting process back to square one.

Three of Iraq's provinces - Anbar, Salaheddin and Nineveh - have Sunni Arab majorities. And in contrast to the boycott calls before the parliamentary elections in January, Sunni Muslim imams and politicians are urging their community to register to vote in the referendum.

Still, gaining a two-thirds vote against the constitution in all three provinces would be difficult.

As the text of the draft appeared in newspapers Tuesday, Salih al-Mutlaq made a bid for support from secular Shiites, pointing out the threat of dividing Iraq.

A key ally for the Sunnis could be Muqtada al-Sadr, the radical Shiite cleric whose militia fought U.S. troops in Najaf last year.

Sadr supporters marched in Baghdad last week denouncing parts of the constitution, including the articles dealing with federalism.