Iraq delayed until Thursday 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 Saddam Hussein's ouster.

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 political 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 U.S.-led invasion in 2003 a timeline for the withdrawal of American troops and offers what Prime Minister Nouri al-Maliki describes as 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 Parliament Speaker Mahmoud al-Mashhadani said political leaders were working toward a settlement that will clear the way for a rescheduled vote Thursday.

"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 — around 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 only be acceptable 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.

Iraq's government has two options if parliament doesn't pass the deal: renew the U.N. mandate governing the presence of U.S. troops in Iraq that expires Dec. 31, or ask them to leave immediately. Al-Maliki and top Cabinet ministers say neither option was good for Iraq.

Already, the ruling Shiite and Kurdish blocs appear ready to grant the Sunni Arabs and smaller groups their demand for a nationwide referendum on the pact to be held no later than July 30 in exchange for their support. If that happens, the deal could be approved by parliament but torpedoed by a "no" vote in the referendum.

In Washington, Secretary of State Condoleezza Rice said the proposed referendum did not necessarily mean the pact will be put off. She said she had spoken to U.S. Ambassador Ryan Crocker in Baghdad and that her understanding is that the referendum process would not delay implementation of the security pact.

White House spokesman Tony Fratto said Washington remained hopeful that the Iraqi parliament would pass the agreement.

"They're going to keep working at it," he said. "It's a very good agreement. It's good for both Iraq and the United States. And so we'll keep an eye on what they're doing and hopefully they'll be able to get it across the goal line."

One of al-Maliki's deputies, Barham Saleh, said late Wednesday that parliamentary blocs were finalizing a political deal ahead of the vote on the security pact.

"We hope that tomorrow the agreement will be presented to parliament as well as an agreement on a package of political reforms that the government and parliament will undertake," Saleh, a Kurd, told Associated Press Television News.

If parliament approves the pact, it must be ratified by the Presidential Council, whose three members each have veto power. Two members support the deal. The third, Vice President Tariq al-Hashemi, is a Sunni Arab who could support it if he believes that parliament's biggest Sunni Arab bloc, the Iraqi Accordance Front, has secured enough political gains in pre-vote dealmaking.

In addition to a referendum on the pact, the Front wants bigger representation for Sunni Arabs in the Shiite-dominated security forces and the release of thousands of detainees, mostly Sunnis, who are held in U.S.-run facilities without charges. Under the security deal, detainees will be handed over to Iraqi authorities if arrest warrants are issued.

Al-Maliki says those demands should not be linked to the pact and has pledged to free detainees who were not involved in the insurgency.