BAGHDAD, Iraq, Aug. 12 - Iraq's leaders said Friday that they had reached a tentative deal to divide the country's vast oil wealth between the central government and the provinces, a potentially significant break in the negotiations over a new constitution.
Under the agreement, oil revenue would be shared by the central government and Iraq's 18 provinces, and split roughly according to their populations. It was unclear which entity would control the money, though one Iraqi leader said it would be the central government.
"The agreement is that the distribution would be under the control of the federal government," said the leader, Saleh Mutlak, a member of the committee charged with writing the constitution.
If it holds, the deal will constitute a major advance in the effort to complete a constitution. The control of oil revenue, which provides the bulk of Iraq's income, could significantly strengthen the hand of the central government over the regions, like Kurdistan and southern Iraq, that are pushing for greater self-rule.
Most of Iraq's oil is concentrated in fields well to the south and north, raising fears, especially among the Sunni Arab population, that the revenues will fall under the control of the Shiite Arabs and the Kurds. Until this week, Kurdish leaders were demanding that they keep at least 60 percent of the money earned from oil in their area, in the north. A Kurdish official said Friday that they had dropped that demand.
"This is a formula that everyone can agree on," said Mahmood Othman, a Kurdish member of the constitutional committee.
Iraq's leaders remained bitterly divided over the question of autonomy for the Shiites in southern Iraq, with Sunni leaders saying the demands of Shiite leaders could lead to the disintegration of the country.
The acrimony followed a public call for a Shiite autonomous region by Abdul Aziz al-Hakim, one of the country's most powerful Shiite political leaders. Shiite leaders have already imposed Islamic rule in many areas of southern Iraq, including restrictions on the rights of women and on personal matters like dress and alcohol consumption.
The staunchest opposition to the drive for Shiite autonomy came from Sunni leaders. The Sunnis, believed to make up about 20 percent of Iraq's population, dominated the country during the rule of Saddam Hussein and long before that. With Kurdish autonomy largely secured in the north, the Sunnis are wary of being left with a weak and disconnected rump state in the center of the country.
Sunni leaders said Friday that they had rejected a proposal circulated by the American ambassador to Iraq, Zalmay Khalilzad, intended to bridge the divide between them and the Shiites. Under the American proposal, the constitution would declare Iraq to be a federal state, but leave the details for the representatives elected in December.
But Sunni leaders rejected that, saying that a Shiite-dominated legislature would be free to run roughshod over the Sunni minority.
The disagreement over Shiite autonomy raises the prospect of a breakdown in the talks over the constitution. The drafting committee missed its Friday deadline for handing a completed document over to the Iraqi National Assembly. Under the rules agreed upon last year, the National Assembly is supposed to approve a final constitution by Monday. It then would go before voters in a nationwide referendum on Oct. 15.
In addition to Shiite self-rule, a number of other issues continue to bedevil the constitution drafters. Principal among them is control over the ethnically divided northern city of Kirkuk. Mr. Othman, the Kurdish leader, said there was broad agreement between Shiite and Kurdish leaders to include language in the constitution that would call for the reversal of the migration of tens of thousands of Arabs to Kirkuk, mostly in the 1980's.
The Arabs who came to Kirkuk typically took the homes of fleeing Kurds, who were expelled from the city en masse during Mr. Hussein's time as Iraq's leader. Under the agreement discussed by Mr. Othman, the Iraqi government would have to reverse the "Arabization" of Kirkuk by Dec. 15, the date for nationwide elections.
Completing such a mass repatriation before the elections would almost certainly restore the city to Kurdish control. But moving an estimated 5,000 to 10,000 Arab families out of the city and resettling them would probably prove extremely difficult.
Mr. Othman said he hoped that the cooperation between Kurdish and Shiite leaders would put pressure on Sunni leaders to make a deal. On Friday, such a prospect did not seem so likely, particularly on the question of Shiite autonomy. In Sunni mosques, even the clerics were urging the faithful to oppose the Shiite demands.
"There is a conspiracy and a scheme to split our country," a Sunni cleric, Sheik Mahmoud al-Sumaidie, told his followers at the Umm al-Qura mosque in Baghdad. "That is what our enemies want from us."