The proposed Iraqi legislation, drafted by the parliamentary bloc loyal to anti-American Shiite cleric Muqtada al-Sadr, was signed by 144 members of the 275-member house, according to parliamentary officials.
The Sadrist bloc, which holds 30 parliamentary seats and sees the U.S.-led forces as an occupying army, has pushed similar bills before, but this would be the first time it persuaded a majority of lawmakers to sign on.
The measure has not yet been introduced in parliament and was unlikely to be passed in its present form. But the signatures reflected growing disenchantment among the lawmakers over U.S. involvement in Iraq and the government's failure to curb the violence in the country.
It also appeared to be part of a campaign by al-Sadr's followers to carve out a strong opposition position after they quit Prime Minister Nouri al-Maliki's Cabinet last month over the government's refusal to demand a timetable for the U.S. to leave.
The White House questioned whether Sadrists had the votes in parliament.
"The president of Iraq, the vice presidents, and the prime minister all support keeping U.S. troops in Iraq," National Security Council spokesman Gordon Johndroe said in Washington. "The Sadrists often makes these claims, yet rarely produce a bill, let alone a majority."
The discussion over a troop withdrawal came as a series of evening explosions rocked Baghdad, killing at least two people. A total of 35 people were killed or found dead nationwide Thursday.
The military announced that three more U.S. troops had been killed. Two soldiers were killed by gunfire Thursday - one in Baghdad and the other in Diwaniyah - and a Marine died Wednesday in combat in Anbar province.
Despite al-Sadr's bill, Shiite parties still represented in the Cabinet are not keen to see U.S. troops leave until Iraqi forces are ready to take over security. Al-Maliki relies heavily on U.S. support to hold his factious administration together.
Ali al-Adeeb, a senior Shiite lawmaker and confidante of al-Maliki, was skeptical about the wisdom of asking foreign forces to leave.
"Their withdrawal will not benefit anyone if our forces are not ready," al-Adeeb said. "There must be a commitment from foreign parties to train our forces."
Kurdish lawmaker Mahmoud Othman said he supported the draft but only on condition that the withdrawal timetable be linked to a schedule for training and equipping Iraq's security forces. "But the sponsors of the legislation did not include our observations in the draft. This is deception," he said. That suggested that some who endorsed the bill will either vote against it or abstain. The proposed bill would require the Iraqi government to seek approval from parliament before it requests an extension of the U.N. mandate for foreign forces to be in Iraq, said Nassar al-Rubaie, the leader of the Sadrist bloc. It also calls for a timetable for the troop withdrawal and a freeze on the size of the foreign forces. The U.N. Security Council voted unanimously in November to extend the U.S.-led forces' mandate until the end of 2007. The resolution, however, said the council "will terminate this mandate earlier if requested by the government of Iraq." The draft bill appeared to be the latest effort by al-Sadr to ratchet up his anti-American rhetoric in an apparent bid to maintain his stature among his followers after disappearing from public view before a U.S.-Iraqi security crackdown began three months ago. Last month, he ordered his six Cabinet ministers to leave the government after al-Maliki refused to put a timetable for a troop withdrawal. The black-turbaned cleric, who the U.S. says is in Iran despite denials by his supporters, ordered his Mahdi Army militia to disarm and stay off the streets to avoid confrontation with the Americans during the current operation. But the Shiite extremists have shown increasing signs of frustration as they face raids and arrests while the bombings largely blamed on Sunni insurgents continue. U.S.-led forces conducted a raid in the Mahdi Army stronghold of Sadr City early Thursday, killing three militants and detaining four as they tried to break up a cell accused of smuggling powerful roadside bombs and other weapons from Iran to fight U.S. forces, the military said. Iraqi police and medical officials said the airstrike damaged three houses and killed eight civilians and wounded nine. The reason for the discrepancy in the two accounts was not immediately clear. The police and medical officials spoke on condition of anonymity because they were not authorized to talk to the media. Local officials also said an American armored vehicle smashed a mourning tent that had been erected to hold bereaved guests of a deceased resident, injuring three people who were sleeping inside. Footage from AP Television News showed a collapsed tent, with its metal support posts bent and the plastic chairs inside splintered. The military did not comment on the incident. The Thursday night attacks in Baghdad began about 9:10 p.m. when a parked motorcycle exploded near a soda shop in the southeastern area of Zafaraniyah, killing two people and wounding four, police said. About 20 minutes later, a suicide car bomber targeted a U.S. convoy in Karamanah Square, a popular area in the mainly Shiite neighborhood of Karradah, police said. The blast sent up huge plume of smoke. The U.S. military said it had no immediate information on the blast. Meanwhile, an al-Qaida front organization, the Islamic State of Iraq, posted a video showing the execution of nine Iraqi security officers who were lined up blindfolded with their hands bound behind them and shot in the back of the head. The authenticity of the video, posted on a Web site where the group often releases messages, could not be independently confirmed.