WASHINGTON – Some 13,000 National Guard troops are receiving notice to prepare for possible deployment to Iraq, making it the second tour for several thousand of them.

The orders had been anticipated, but the specific units were not announced until Monday. They are the Army National Guard’s 39th Infantry Brigade Combat Team, based in Little Rock, Ark.; 45th Infantry Brigade Combat Team, Oklahoma City; the 76th Infantry Brigade Combat Team, Indianapolis; and the 37th Infantry Brigade Combat Team, Columbus, Ohio.

The units would serve as replacement forces in the regular troop rotation for the war, and would not be connected to the recent military buildup for security operations in Baghdad, the Pentagon said.

One unit would deploy in December and the remaining in 2008, the Army said in a statement.

”They are receiving alert orders now in order to provide them the maximum time to complete their preparations,” the Defense Department said in a separate statement. ”It also provides a greater measure of predictability for family members and flexibility for employers to plan for military service of their employees.”

The final determination on whether the units will deploy will be made based on conditions on the ground in Iraq, officials said.

The troop alerts come as President Bush and Congress wrestle over legislation that would set timelines for troop withdrawals from Iraq.

Bush asked for more than $100 billion to pay for the wars in Iraq and Afghanistan this year. Congress has approved the money, but the Senate added a provision calling for most U.S. combat troops to be out of Iraq by March 31, 2008. The House version demands a September 2008 withdrawal. Bush has vowed to veto any legislation that includes such deadlines.

Smaller units and individual troops from the Guard have already returned to Iraq, and some active duty units have served multiple tours. The Army said some of the troops being alerted now have not yet served in Iraq, but some have served in the campaign in Afghanistan or elsewhere:

• The 39th Infantry Brigade Combat Team last deployed as part of the 1st Cavalry Division from February 2004 to February 2005, serving in Baghdad’s Green Zone and in Taji.
• Since November 2002, various elements of Indiana’s 76th Infantry Brigade Combat Team have deployed at one time or another to Iraq and Afghanistan. Their last brigade-level rotation was in support of the Afghan campaign from May 2004 to August 2005.
• The 45th most recently served in Afghanistan, deploying in the fall of 2003 to support the Afghan National Army.
• The 37th Infantry Brigade Combat Team last deployed to support operations in Kosovo as part of the United Nations mission from August 2004 to February 2005. Due to reorganization, the brigade now includes citizen soldiers from Ohio and Michigan.

”These outstanding citizen soldiers, their family members and employers continue to make great sacrifices for the good of our country and they appreciate and acknowledge the continued support of the American people,” the Army said.