Washington ? U.S. military commanders Wednesday announced that they would increase the number of troops in Iraq to 150,000 — the highest level since the March 2003 American-led invasion — in an effort to meet an expected increase in insurgent violence as next month’s Iraqi national election draws near.

The buildup will be achieved by extending the stay of about 10,400 troops already in Iraq and dispatching 1,500 more from the United States.

Wednesday’s announcement follows the recent U.S.-led offensive that broke the insurgents’ hold on the city of Fallujah. While that battle was in progress, rebel attacks increased elsewhere in the country, and there were concerns that the gains made in Fallujah could erode without a larger U.S. military presence.

“It’s mainly to provide security for the elections, but it’s also to keep up the pressure on the insurgency after the Fallujah operation,” U.S. Army Gen. David Rodriguez said Wednesday during a Pentagon news briefing. “But both those things provide better security for the elections.”

In recent months, the Iraqi interim government and the U.S. military have stepped up recruitment and training of Iraqi troops in the hope that they could play a larger role as the Jan. 30 election approaches. But recent insurgent attacks have targeted the Iraqi forces, undercutting their ability to assume as much of a burden as some had envisioned.

The U.S. force in Iraq has never exceeded 148,000, the total at the time President Bush declared major combat operations over on May 1, 2003. After rising to 150,000 before the election, the troop count is expected to return to its current level of about 138,000 in March, Rodriguez said. But he cautioned that the plan was flexible.

To boost current troop levels, commanders are extending the tours of three Army units and one Marine unit until March. Those units and the approximate number of affected forces include:

• 4,400 soldiers from the Army’s 2nd Brigade of the 25th Infantry Division, which is based in Hawaii. They would have left Iraq in January.
• 3,500 soldiers of the 2nd Brigade of the 1st Cavalry Division, who also will stay through March. Those soldiers were originally scheduled to return to Fort Hood, Texas, in November.
• 2,300 Marines from the 31st Marine Expeditionary Unit, based in Japan. They would have left Iraq next month.
• 160 soldiers from the Army’s 66th Transportation Company. They were set to return to their German base in January.

In addition, 1,500 soldiers from the 82nd Airborne Division based at Ft. Bragg, N.C., will deploy to Iraq in the coming days and be in place by mid-month. These troops are part of the division’s rapid deployment brigade, which is designed to move quickly to foreign trouble spots.

Rodriguez said the 82nd soldiers would stay in Iraq at least four months.

For the soldiers and Marines who have suddenly learned that their stays have been extended, Wednesday’s announcement was likely to be a heavy blow. Many had expected to leave within weeks, and one unit — 2nd Brigade of the 1st Cavalry Division — has now been extended a second time.

Originally, that unit was scheduled to return home in November, a deadline that was earlier moved to January 2005. Now the brigade will stay an additional two months.

The announcement of extended deployments came after a month in which U.S. troop deaths equaled a record. The death toll in November was 135, the same as in April 2004. At least 1,255 U.S. troops have died in the war, 984 of them in combat.