JACKSON (AP) — A Mississippi Army National Guard brigade made up of nearly 3,500 soldiers was put on alert Monday that it could deploy to Iraq for the second time as early as 2009.

It would be the second tour of duty for hundreds of Mississippians in the 155th Brigade Combat Team. The soldiers spent most of 2005 in Iraq during the largest deployment of Mississippi Guard soldiers since World War II.

That deployment effected nearly the entire state, drawing soldiers from at least 49 different communities. About half of those soldiers remain in the brigade, said Maj. Gen. Harold A. Cross, Mississippi’s adjutant general.

Cross told The Associated Press on Monday that the Department of Defense issued an alert, not a mobilization order, which would have meant deployment was imminent.

‘‘This is a heads up to start getting ready, that we may need you sometime in the summer of 2009 or later,’’ Cross said. ‘‘This is the first phase to let them know that they are scheduled for deployment in the future.’’

The likelihood that the brigade will be sent to Iraq depends on the situation there when the time comes, Cross said. The alert directs more money and equipment to the unit for training.

Staff Sgt. Mark Smith, a 23-year-old criminal justice major at the University of Mississippi, said he was not surprised by the alert. He served with the 155th the first time in Iraq and is ready to go again if needed. He just signed up for six more years in the Guard, though he wishes wounded vets had access to better health care.

‘‘There’s good things and there’s bad things about the war,’’ he said. ‘‘But it’s not our job to be political. We made oaths and it’s our job to fulfill them.’’

It’s difficult to know exactly how many members in the 155th would deploy for the second time. About 50 percent of the soldiers have already left the brigade and another 15 percent to 20 percent likely will have been lost to attrition by 2009, Cross said. Recruitment in the Mississippi Guard has recently picked up after a dip following Hurricane Katrina in August 2005.

‘‘We’ll have quite a number of soldiers, senior officers, and senior NCOs (noncommissioned officers) who have been in combat before,’’ Cross said. ‘‘But we’ll have quite a number of new soldiers who have never been in combat if we do deploy in 2009.’’

The deployment of such a large group of Guard soldiers creates unique challenges at home for employers and families, who sometime have to adjust to less income.

Among those who deployed with the 155th the first time were: Leslie Southwick, a former state judge who has since been elevated to the U.S. 5th Circuit Court of Appeals in New Orleans, a sheriff, public school principals and teachers and dozens of police officers and firefighters.

Southwick is still in the Guard but is no longer a member of the 155th, said Tim Powell, a Guard spokesman. Southwick did not immediately respond to a message left Monday at his home.

National Guard brigades from Oregon and Wisconsin were also put on alert Monday for duty in Iraq. Brigades from Florida and Georgia were told to prepare for Afghanistan. In all, the alerts for duty in Iraq affect about 8,000 men and women, the Defense Department said.

The soldiers headed to Iraq will train for ‘‘security force’’ missions like defending bases and guarding convoys. However, it is difficult to know exactly how the soldiers will be used so far in advance. Conditions on the battlefield are constantly changing and the military is forced to adapt.

‘‘The Department of Defense is trying its best to give units as much advance notice as possible for obvious reasons — the equipment resetting and training — but also to let families and employers know as far in advance as possible,’’ Cross said.

Col. Bill Glasgow, commander of the 155th, said the soldiers have been in continuous training and will be prepared for anything that comes their way. Like many others in the 155th, Glasgow has already been to Iraq.

‘‘They did a tremendous job’’ in the first deployment, Glasgow said. ‘‘These are great soldiers.’’

Fourteen Mississippi Guardsmen in the 155th died in Iraq. More than a dozen others attached to the brigade from other states lost their lives as well.

The soldiers came home to widespread praise. Individual medals awarded to the troops in the 155th included 123 Purple Hearts, 328 Bronze Stars, 2,000 Combat Badges and one Silver Star.

‘‘In the tradition of the 155th, we’ve accomplished every mission asked of us. We’ll have our soldiers ready to fight, our equipment ready and our powder dry,’’ Cross said. ‘‘We’ll go do whatever the president has asked us to do.’’

There also are about 260 Mississippi Guard soldiers already deployed. Cross said he is going to Iraq this weekend to visit some of them.

The full 4,200-member 155th that deployed in 2005 was made up of soldiers from Pennsylvania, California, Washington, Texas, Puerto Rico, Virginia, Missouri, New Jersey, South Carolina, Vermont, Utah and Arkansas.