The Cabinet approved the agreement last weekend, meaning the pact stands a good chance of passage in 275-seat parliament where the government's parties dominate.

But the vocal opposition in parliament could mean a narrow victory for the government in the vote, which would cast a shadow on the legitimacy of the deal that al-Maliki has said should be approved with a broad consensus.

Iraq's most influential Shiite cleric, Grand Ayatollah Ali al-Sistani, said the deal would be acceptable only if approved by a wide margin in parliament. Al-Sistani enjoys enormous influence among Iraq's Shiite majority. He could bury the deal if he speaks publicly against it.

How the deal fares in parliament will also have implications for the fortunes of Iraq's major parties in provincial elections on Jan. 31 and a general election late in 2009.

The Sadrists hope their anti-American stance will win them votes of Iraqis who see the Americans as occupiers who plan to stay indefinitely.

But al-Maliki's Dawa party and the Supreme Islamic Iraqi Council, its senior government partner, hope passage by a wide margin could win them votes as the parties that engineered a timetable for the Americans' departure.

If the agreement passes the legislature, it will go to the president and his two deputies for ratification. Each one has veto power.

Shiite coalition parties, which have 85 seats, and the Kurdish bloc, with 54, firmly support the pact, and their votes alone amount to a thin majority. They might also pick up support from smaller parties.

The position of their Sunni Arab allies, the three-party Iraqi Accordance Front, is less certain and many of those 44 lawmakers might not back the deal.

Beside the Sadrists, who have about 30 lawmakers, the small Shiite Fadhila party, which has 15 seats, and a small Sunni Arab bloc with 11 seats are firmly opposed to the deal.

Also Thursday, the U.S. military said a leader of al-Qaida in Iraq, blamed in the 2004 abduction and murder of Army reservist Staff Sgt. Matt Maupin of Batavia, Ohio, had been killed.

The military said Hajji Hammadi also was the mastermind of a June 26 attack that killed three U.S. Marines, two interpreters and more than 20 Iraqis in western Anbar province.

It said U.S. forces killed Hammadi and another armed insurgent on Nov. 11 in Baghdad.