Sunni leaders reacted with fury at the proposition, claiming that it would inflame the insurgency and trigger civil war and vowed to defeat the charter at a national referendum later this year unless demands for federalism were dropped.

But Shia leaders, determined not to miss the deadline, presented the draft to parliament minutes before midnight. To loud applause, the speaker announced that the deadline had been met. Then to stunned confusion, he dismissed parliament without a vote, calling for three more days of talks between political leaders. But as the events of the evening sank in, it remained unclear what could be done to win over the recalcitrant Sunnis.

Moments after parliament was adjourned, Sunnis issued a statement rejecting the draft because a consensus had not been reached. “If it passes, there will be an uprising in the streets,” Saleh al-Mutlak, a senior Sunni negotiator, said. He added that further blockage of a deal could trigger elections to a new interim assembly, a scenario that most parties — particularly the Shias — wish to avoid.

Even after printing their final draft, Shia and Kurd leaders had continued trying to win over the Sunnis, but officials said the sticking points had been federalism, the mechanism for allowing regions to devolve and deBaathification — the banning of former regime figures from public office.

Sunnis vehemently opposed attempts by the Shias and the Kurds to carve out their own powerful federal regions, fearing they could be left high and dry while the oil-rich North and South go their own way. They also fear that deBaathification could keep their minority out of official positions.

The new delay will come as a bitter disappointment to Washington, which had exerted heavy pressure on the factions to reach an agreement and dropped its opposition to a strong role for Islam, leading to accusations of a sell-out. The Bush Administration badly needs to demonstrate political progress in Iraq to counter growing domestic opposition to the costly military occupation.

The Administration hoped that involving Iraq’s Sunni minority in the constitutional drafting process would help to bring it back into the political mainstream and sap the violent insurgency.

But that prospect looked remote last night as Sunnis threatened to derail the draft constitution should it make it through parliament with the issues of contention unchanged. “All the history of Iraq’s problems is contained in this constitution — racism, sectarianism and secession,” Hussein Shukur al-Falluji, a Sunni delegate, said. “If they pass this constitution, then the rebellion will reach its peak.”

“We will not be silent,” Soha Allawi, another Sunni Arab member of the drafting committee, said. “We will campaign to tell both Sunnis and Shias to reject the constitution, which has elements that will lead to the break up of Iraq and civil war.”

The Shias would have faced little difficulty ramming the constitution through a parliament they control, but almost certainly backed off because the Sunnis could defeat the draft in October’s scheduled referendum. If two thirds of voters in at least three provinces reject the document, the constitution will fail. The Sunnis have such a majority in three provinces and have started a vigorous “no” campaign.

The draft was also said to reflect a Kurdish and American compromise over Islamic law. “Islam is a main source for legislation and it is not permitted to legislate anything that conflicts with the fixed principles of the rules of Islam,” it read.

But it also apparently insists that all laws must respect “democracy and human rights”, a phrase insisted on by America.

Kurdish leaders said that they backed the agreement, saying that the provision on federalism was enough to satisfy their demands for guarantees that they would retain the broad autonomy they already have in the North.

The Kurds and the Shias also agreed to distribute Iraq’s oil and other natural wealth “according to the needs” of the central Government and the provinces. The status of the oil-rich city of Kirkuk will be determined by the end of 2007.

Last night’s deadline was the second after negotiators failed to agree last week, to the disappointment of the Americans. Parliament then voted to extend deliberations by a week.