The U.S. Army will announce today a plan for rotating fresh troops into Iraq and bringing home those who have served the longest. The plan calls for maintaining troops at their current level of about 145,000 by rotating units on a one-for-one basis.

Under the plan, soldiers of the 3rd Infantry Division, who have been in Iraq longer than any other conventional unit, will be replaced by a Stryker brigade, elements of the 82d Airborne Division and some National Guard units, defense officials told The Associated Press yesterday.

Pentagon officials would not say which of two brigades equipped with the new Stryker armored car will be sent to Iraq, but it likely will be the 3rd Brigade of the 2nd Infantry Division, stationed at Fort Lewis, Wash. The National Guard units have not been identified.

Soldiers from the 101st Airborne Division will be replaced by soldiers from the 1st Infantry Division, which is based in Kansas and Germany. No timetable has been announced for when the rotation will begin.

Soldiers sent to Iraq under the new rotation plan will serve one-year tours. One year was the standard length for combat tours in the Vietnam and Korean wars, but in recent years Army deployments overseas rarely have extended beyond six months.

Some soldiers from the 3rd Infantry Division have been in Kuwait or Iraq since September and took part in the initial invasion of Iraq. They had been told twice that they were coming home, only to have their time in Iraq extended. This has prompted some of them, and their families, to publicly complain.

"Our morale is not high or even low. Our morale is nonexistent," one 2nd Brigade soldier said in an email. "Our troops and equipment are worn out."

Last week, ABC News prominently featured gripes by two 2nd Brigade soldiers, neither of whom was identified. "If [Defense Secretary] Donald Rumsfeld was here, I'd ask him for his resignation," one said.

The 3rd Infantry's time in Iraq was extended because of the upsurge in violence since June, and because fewer allies than had been expected have been willing to send peacekeeping troops.

The division could not be relieved sooner because the U.S. military has too many commitments for too few troops, said retired Army Lt. Col. Ralph Peters, a frequent writer on military affairs.

"We've got a 15-18 division strategy with a 10 division force," Peters said. "It's time for the Pentagon to face up to the fact that we don't have enough bodies."

Nearly half of the Army's 10 divisions and three separate brigades are deployed in Iraq, Afghanistan, Kosovo or South Korea. The problem in Iraq is exacerbated because civilian aides to Rumsfeld didn't pay heed when Army generals told them nearly 200,000 troops would be needed for the occupation, at least in its initial stages, Peters said.

Nevertheless, the press can exaggerate morale problems, he said.

"My friends in Iraq resent the implication that morale is bad," Peters said. "A reporter can always find a soldier who is [ticked] off. But that doesn't mean the whole occupation is a bust."