Iraqi lawmakers will vote Saturday on how to break a deadlock over a key election law after a vice president vetoed the legislation, causing a crisis that could delay a national vote scheduled for January and affect the timetable for an American troop withdrawal.

Iraq's fractious parliament was looking at two options — sending the same law back to the three-member presidency council, where it is likely to be vetoed again — or amending the law to address the concerns of Vice President Tariq al-Hashemi.

Under the constitution, parliament can override a second veto with a three-fifths majority, thereby passing a law seen as vital to Iraq's ability to move toward full sovereignty and political stability after years of bloodshed.

Al-Hashemi, a Sunni Arab, wants the law to allocate more seats to Iraqis living abroad, many of whom are Sunnis who fled the war. The devastating attacks that were so routine in Iraq have become far less common, but al-Hashemi's objections reflect how hard it is for Iraq's ethnic and sectarian factions to reconcile.

Speaker Ayad al-Samarie said Thursday that political blocs agreed to vote after failing to craft an immediate solution to the vice president's demand. Al-Hashemi's veto was welcomed by supporters as a legal right and by opponents as an attack on Iraq's fledgling democracy.

"Basically, we did not find any proposal that enjoys agreement," al-Samarie said. "So it was decided to resort to voting on the veto of the presidency."

The 275-seat parliament could muster the numbers necessary to override a second veto if most Shiite and Kurdish lawmakers choose to do so, but that outcome would fail to ease the sense of alienation of many Sunni Arabs.

The Sunni minority dominated Iraq until a U.S.-led invasion toppled Saddam Hussein in 2003, and boycotted elections in 2005 ahead of the run-up to the most vicious sectarian violence of the war. A Shiite-led government now runs the country.

A return to the intense violence of a couple of years ago is unlikely, and the U.S. military believes it can stick to its timetable of withdrawing all U.S. combat troops by the end of August 2010, and the rest of its personnel by the end of 2011.

Still, U.S. military officials have said they will begin to draw down combat forces about 60 days after the election, and the possibility of a vote delay could compel commanders to reassess the plan just as Washington is pondering a buildup of forces in Afghanistan.

Iraq's political and legal institutions buzzed with debate and some confusion on Thursday, a day after al-Hashemi's veto. The Supreme Federal Court cited the constitution as saying all Iraqis, whether they live in the country or outside its borders, should be represented in the parliament.

Some lawmakers interpreted the court's statement as a conclusion that al-Hashemi's veto was unconstitutional, while those in the vice president's camp said the opposite.

Iraq's electoral commission said it has suspended preparations for the vote, which the constitution says should be held by the end of January. With time running out, legislators who spent weeks haggling over the election law — only to see it vetoed — boiled with frustration.

"The atmosphere prevailing in today's meetings was one where disputes went back to the way they were when we first discussed the draft law," said Abbas al-Bayati, a Shiite lawmaker.