Also, about 2,300 members of the 31st Marine Expeditionary Unit, based in Okinawa, Japan and in Hawai'i and California, will stay until mid-March instead of leaving in January.

The extensions come as the United States is expanding its military force in Iraq by 12,000 troops, to the highest level since the war began in March 2003, in order to bolster security in advance of national elections, officials said today.

The expansion will be achieved by sending about 1,500 troops from the 82nd Airborne Division in Fort Bragg, N.C., this month and by extending the combat tours of about 10,400 troops, including thousands of Hawai'i-based troops, already in Iraq.

Brig. Gen. David Rodriquez, deputy operations director of the Joint Staff, told reporters that these moves would increase the size of the American force in Iraq from 138,000 today to about 150,000 by January.

That is the highest number of U.S. troops in Iraq since the invasion, he said. By May 2003, when President Bush declared major combat operations over, there were about 148,000 U.S. troops in Iraq, he said.

Other extensions listed:

• About 3,500 soldiers of the 2nd Brigade of the 1st Cavalry, will be extended until March. These are the soldiers who originally were told they would be leaving Iraq in November.
• About 160 soldiers of the 66th Transportation Company, based in Germany, was due to depart Iraq in early January but instead will stay until early March.

The moves announced today are in line with expectations — a combination of holding some troops in Iraq longer than scheduled and sending some fresh forces from the United States.

Officials have said they were considering sending some elements of the 3rd Infantry to Iraq earlier than scheduled, as part of a force-bolstering plan. But Rodriguez said it was decided that no units will have their deployments accelerated as part of the pre-election security effort.

Security problems are most severe in the area north and west of Baghdad, as well as in the capital itself. Voter registration has not yet begun in the more unstable cities such as Fallujah and Ramadi, west of Baghdad.