"The meeting of leaders was delayed from Friday to Sunday so that a greater number of participants could attend," a spokesman at President Jalal Talabani's office said.
The meeting is convened by Talabani in a bid to break the deadlock on drafting a new constitution and resolve outstanding questions on which members of the constitutional committee have so far failed to agree.
The issues to be resolved include federalism, official languages, the relation between religion and state, the name of the republic, the rights of women and the question of the oil-rich centre of Kirkuk which Kurds want included in their own autonomous region.
Iraqi leaders have pledged to draft a new constitution by 15 August.
Mahmud Othman, a Kurdish member of the constitutional committee, told AFP that the national conference was delayed because of an emergency meeting on Saturday of the Kurdish autonomous parliament to discuss the constitution.
Kurdish leader Massud "Barzani cannot come to Baghdad before Sunday" because of the parliamentary meeting, Othman said.
The national leaders' conference is due to report back by 12 August, and any matter still unresolved will be put to the full parliament for decision by majority vote.
Last 10 days saw the some of the
deadliest violence since March 2003
A national referendum on the constitution is planned for 15 October, to be followed by general elections in mid-December and the inauguration of a new government at the start of next year.
Iraq will be a parliamentary republic with a strong prime minister and a figurehead president, according to the latest draft of the constitution.
News of the delay in holding the crucial conference came against a background of unremitting violence in the country where at least 38 US military personnel have died in the last 10 days -- one of the deadliest insurgency bouts since the March 2003 invasion.