BAGHDAD - Iraqis will vote in a general election on January 21 now that parliament has passed a law needed for a vote to take place, the head of the country's electoral commission said on Monday.

The assembly ended weeks of disagreement about the fate of the disputed city of Kirkuk to pass the electoral law on Sunday.

The ballot was originally meant to take place on January 16 but electoral authorities said the delay in passing the law had made it impossible to organize it by then.

Faraj al-Haidari, head of the electoral commission, told Reuters the new date of January 21 needed to be approved by the presidency council of President Jalal Talabani and two vice-presidents.

I don't think that date will change, he said.

Prolonged arguing over the law had cast doubt on the U.S. military's plans to end combat operations in Iraq by August 31, 2010, ahead of a full withdrawal by the end of 2011.

The election law had been held up by disagreement over how to conduct the vote in Kirkuk, a northern city that is surrounded by oilfields.

Kirkuk is viewed by ethnic Kurds as their ancient capital, and they want to make it part of their northern region. Kurdish leaders wanted to use up-to-date voter rolls in the election to reflect an increase in their numbers there since 2003, the year the U.S.-led invasion toppled Saddam Hussein.

Arabs and Turkmen say the city should remain under central government authority and believe Kurds have deliberately tipped the demographic balance. They hoped older voter records would be used scrutiny of voters' registrations would be guaranteed.

The law used current voter registrations but made the election results subject to a review if there were an unusual increase in registered voters in the past five years. The consequences of a possible review were not spelled out.

Haidari said the next parliament would have 323 seats compared with 275 now to take account of an increase in population since the last election in 2005.

(Reporting by Muhanad Mohammed; writing by Michael Christie; editing by Andrew Dobbie)