Iraqi legislators were to try again today to discuss the security agreement, but it was clear from yesterday's session that political factions were more divided on the issue than when it was given to parliament members earlier this week.

The discord does not bode well for passage by Tuesday, when lawmakers are expected to begin a nearly monthlong break. If the pact is not approved by the end of the year, it would leave U.S. forces without legal standing to be in Iraq come Jan. 1.

The session was chaotic from the start, with lawmakers shouting at one another. Speaker Mahmoud al-Mashhadani added to the din by repeatedly yelling at legislators to sit down or keep quiet, but failed to restore order.

Lawmakers loyal to Shiite Muslim cleric Muqtada al-Sadr, who wants U.S. forces to leave Iraq immediately, accused security guards in parliament of roughing up one of their legislators when he tried to prevent debate.

"Terrorism has entered the hall of the parliament!" Sadr-bloc lawmaker Aqeel Abdul Hussein shouted after lawmakers spilled out of the meeting hall without discussing the agreement.

Lawmakers from three other political blocs joined the Sadrists in condemning what they called bullying by bodyguards inside parliament, and they vowed to boycott further sessions.

The groups do not have enough combined seats to prevent a quorum in the 275-seat legislature, assuming enough other lawmakers show up, but their action will deny Prime Minister Nouri al-Maliki the backing he needs to avoid deepening rifts that have hobbled reconciliation efforts.

Maliki also faces provincial and national elections next year and cannot afford to be seen as backing a plan that foes describe as overly favorable to the Americans.

U.S. officials also are pushing for passage of the status-of-forces agreement, or SOFA. In Washington, Secretary of State Condoleezza Rice, Defense Secretary Robert M. Gates, and Marine Gen. James E. Cartwright, vice chairman of the Joint Chiefs of Staff, were briefing members of Congress on the plan yesterday.

If Iraqi lawmakers reject the pact, it would be an embarrassment to U.S. officials, who spent nearly nine months in negotiations with Iraqi officials and made several concessions to win Maliki's backing.

When Maliki's cabinet approved the pact, 27-1, Sunday and passed it on to parliament, U.S. officials had hoped it was a sign Iraq's factions could rally behind a common goal of Iraqi sovereignty.

The U.S. concessions included agreeing to a firm deadline for the withdrawal of American forces: Dec. 31, 2011. The United States also agreed to pull its combat troops out of Iraqi cities, towns and villages by the end of June 2009.

"I think the Sadrists are the main party opposing the U.S. presence, in any form and for any length of time," said Joost Hiltermann of the International Crisis Group, a Brussels-based think tank. "Anyone else who might vote against the SOFA now is probably just trying to show his nationalist self before the elections."

Shiite coalition parties, with 85 seats, and the Kurdish bloc with 54, firmly support the pact, and their votes together amount to a thin majority.

But politicians from the Sadr bloc, who number 32 in parliament, made clear yesterday that they would do everything possible to prevent the bill from being debated.

As Speaker Mashhadani attempted to open discussions, he was shouted at by legislators. "We must act civilized in front of the world! Stop this chaos!" he yelled, shaking his hand at a Sadr lawmaker who continued shouting above him. "We can't go on like this!" Lawmakers from other blocs joined in the chaos.

Salah Mutlaq, a Sunni lawmaker, demanded to know why all the country's political blocs had not been brought into the loop as the pact was being negotiated. "It's hard to pass such legislation under these conditions," he said.

U.S. negotiators say there is no alternative, except extending the U.N. mandate that authorizes the U.S. presence in Iraq through Dec. 31 or ceasing all U.S. military operations in Iraq as of that date.