BAGHDAD - Iraq will be unable to hold a national election in January as planned, a poll official said on Tuesday, heaping more uncertainty on a vote meant to cement democracy and pave the way for a partial U.S. troop withdrawal.

The general election was supposed to be held between January 18-23, but Iraq's Vice President Tareq al-Hashemi, a Sunni Muslim, last week vetoed a law needed to hold the polls on grounds that Iraqis abroad were under-represented.

Hundreds of thousands of Iraqis fled the sectarian violence triggered by the 2003 U.S. invasion of Iraq, and many are Sunni.

Parliament returned the law to the presidential council, including Hashemi, on Monday, but deliberately failed to address his concerns and in all likelihood it will be vetoed again.

In all cases the possibility of holding the vote in January is over, said Faraj al-Haidari, head of the electoral commission.

In theory the election law must be passed 60 days before the vote, making Tuesday the last day lawmakers can reach agreement to meet the January 23 proposed election date.

But after a heated parliamentary session on Monday, the fractious parliament seemed more divided than ever.

Lawmakers belonging to Iraq's majority Shi'ite community and minority Kurdish community voted for amendments to the election law that would weaken Sunni voter representation, a move some said was meant as a poke in the eye for Hashemi.

Sunni lawmakers staged a walk out of the session and the next sitting is not scheduled until December 8, although the speaker could call for an extraordinary session to end the impasse.

The amendment made by the parliament yesterday is unconstitutional, unfair and contradicts parliamentary standards, said a statement from Hashemi's office, where Sunni lawmakers are planning their next move.

ETHNO-SECTARIAN WOUNDS

The row threatens to re-open ethno-sectarian wounds among Iraq's Shi'ites, Sunnis and Kurds which have only just begun to heal after years of bloodshed. Investors, eyeing Iraq's vast oil wealth and lucrative oil field development contracts but nervous about security, will also be watching the elections closely.

One prominent Sunni lawmaker called for demonstrations against the amended election law, which he called a big crime.

The U.S. military plans to end combat operations by the end of next August before a full withdrawal by 2012, but is waiting to see whether Iraq's fragile stability holds after the polls, the country's first general election since 2005.

The U.S. build-up of troops and hardware in Afghanistan partially hinges on pulling assets out of Iraq first.

Washington has lobbied for the polls to be held on time. A delay beyond January would violate Iraq's constitution, setting a precedent that could encourage autocratically-minded Iraqi leaders to flout the law in the future, analysts say.
Some slippage is OK, but we don't want a lot of slippage, so I hope they look carefully at this and I hope they can get moving, U.S. ambassador Chris Hill told reporters.

U.S. Secretary of State Hillary Clinton said on Monday the United States would present a number of ideas to help break the deadlock.

(Additional reporting by Aseel Kami, Writing by Mohammed Abbas: Editing by Michael Christie and Angus MacSwan)