BAGHDAD — Iraq delayed until today a crucial vote in parliament on a pact that would keep U.S. troops in Iraq through 2011 after lawmakers, many of them Sunni Arabs, demanded concessions from the Shiite-led government in return for supporting the deal.

The one-day delay and Wednesday's backroom haggling highlighted Iraq's deep divisions, as well as the fluid and often chaotic nature of its politics nearly six years after the U.S.-led invasion that ousted Saddam Hussein.

In the past, sectarian-based disputes and other quarrels among Iraqi politicians have stalled efforts to achieve national reconciliation, although some key compromises have been achieved. While the country appears to be emerging from years of intense violence, mistrust among key factions that seek to preserve or advance their own interests has slowed progress.

This time, a longtime Iraqi goal — a clear plan for the departure of foreign forces — is at stake.

The proposed security agreement provides for the first time since the 2003 invasion a timeline for the withdrawal of U.S. troops and offers what Prime Minister Nouri al-Maliki calls a path toward full sovereignty for Iraq.

Under the deal, U.S. forces will withdraw from Iraqi cities by June 30 and the entire country by Jan. 1, 2012. Iraq will also have strict oversight over U.S. forces. The U.N. mandate that currently governs the conduct of American troops gives them freer rein, leading to Iraqi complaints that they are an occupying force intent on preserving U.S. interests in the Middle East.

Lawmakers arrived at parliament for the planned vote Wednesday, but Speaker Mahmoud al-Mashhadani said political leaders were working toward a settlement that will clear the way for a rescheduled vote today.

"We have just been told that the general climate is definitely moving toward a solution," said the speaker, adding that all but one of the issues preventing a vote from occurring were settled.

He did not identify the issue. But senior lawmaker Ayad al-Samarraie said it was a demand by his Sunni Arab bloc to remove all restrictions on the reinstatement of former members of Saddam's now-outlawed Baath Party in government jobs, and the dissolution of a special criminal court that tried Saddam and sentenced him to death along with several top officials of his regime.

Al-Maliki's ruling coalition appears to be assured of a slim majority in the 275-seat legislature — about 140 seats — if the security agreement is put to a vote, but he is seeking a bigger win that transcends religious and sectarian divisions and reinforces the legitimacy of the pact.

Al-Maliki's dilemma has been deepened by the concerns of the country's most influential Shiite cleric, Grand Ayatollah Ali al-Sistani, who has indicated that the deal would be acceptable only if passed by a comfortable majority. The cleric is revered by Iraq's majority Shiites and he could sink the deal if he publicly speaks against it.