National Guard combat brigades from Georgia, Louisiana and Mississippi will be put on active duty in about a week for possible deployment to the Persian Gulf, the Army said yesterday. They will be augmented by National Guard combat units from Alabama, South Carolina and Texas to create a combined fighting force of about 15,100 soldiers, the Army said.

Separately, the Air Force announced it was sending an unspecified number of OA-10 low-level observation aircraft to the Arabian Peninsula for Operation Desert Shield, and the Navy ordered to active duty 875 reservists from 13 states and the District of Columbia. The Air Force OA-10 planes, which are used to direct air and ground fire at enemy armored vehicles, are deploying Saturday from Davis-Monthan Air Force Base, Ariz.

Included in the Army statement was the first official mention that two active divisions -- the 4th Infantry Division (Mechanized) of Fort Carson, Colo., and the 5th Infantry Division (Mechanized) of Fort Polk., La. -- may be sent to the gulf as further reinforcements beyond the deployments already announced.

Maj. Joseph Allred, an Army spokesman, said deployment of the divisions was "an option" now available.

The Guard brigade from Mississippi will be assigned to the 4th Infantry Division and the unit from Louisiana will be made part of the 5th Infantry Division, bringing both of those heavy units to full three-brigade strength, the Army said.