By Paul Tait

BAGHDAD, Dec 9 (Reuters) - About 1,400 U.S. soldiers will launch a fresh assault next week against al Qaeda fighters who are regrouping in areas south of Baghdad, where an Iraqi police chief was assassinated on Sunday, U.S. military commanders said.

The new offensive, known as Operation Marne Roundup, will begin on or about Dec. 15 and will target Sunni Islamist fighters in small hamlets and fishing villages along the Euphrates River valley in Babel province south of Baghdad.

Two battalions of about 700 soldiers each will be deployed at the start of the operation, during which a patrol base will also be established in the area from which U.S. and Iraqi soldiers will operate in the area.

"That is where al Qaeda in desperation is trying to find a location to consolidate their weapons and develop their plans," Colonel Tom James, who will command the operation, told a small gathering of journalists.

Al Qaeda and other Sunni Islamist fighters have been pushed out of western Anbar province, once the most dangerous area of Iraq, and other areas since a security crackdown designed to avert sectarian civil war began in February. A build-up of 30,000 extra U.S. troops and the growth of "concerned local citizens" security patrols, pioneered last year in Anbar, have pushed al Qaeda into northern Iraq and small pockets south of Baghdad, the U.S. military says.

The number of attacks across Iraq have fallen by 60 percent since the troop build-up was completed in mid-June, but U.S. commanders say al Qaeda remains a dangerous enemy and will attempt to launch large-scale, "spectacular" attacks.

Major-General Rick Lynch, commander of U.S. forces in central Iraq, said intelligence suggested 30 al Qaeda fighters were in the area where the new assault will be launched.

"Over time we'll be able to declare victory over the insurgency, but it's not going to happen any time soon. The enemy's still out there," Lynch said.

Hours after Lynch spoke, a roadside bomb killed Major-General Qais al-Mamouri, the police chief of predominantly Shi'ite Babel, near the local capital Hilla, police said.

The operation will be the seventh of its kind launched by U.S. forces in an area stretching from Baghdad's southern outskirts through central Iraq to the Syrian border in the west and the Iranian border to the east.

James said it would involve two battalions, one of which would establish a blocking position in the north of the Euphrates Valley as the other pushes along the valley.

"The plan is designed to catch them as they egress, not giving them free sanctuary to reposition," he said.

Lynch said attacks had fallen 63 percent between June, when the troop build-up was completed, and November in his area of command. He said there were 19,602 contracted "concerned local citizens" manning 825 checkpoints in his region.

U.S. military casualties in the area fell 62 percent and civilian casualties were down by 76 percent in the same period.

Lynch said falling violence and the success of the local citizens programme were proof that Sunni Arab and Shi'ite militants could be drawn away from sectarian violence.

"There are still pockets out there that are irreconcilable and they have to become either dead or detained," Lynch said. (Editing by Caroline Drees)

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