President Bush has approved a partial mobilization of U.S. military reserve forces in the wake of Tuesday's terrorist attacks in New York and Washington.
A Pentagon statement says the president has given defense officials the authority to call up to 50,000 reservists to active duty.
But the statement says the armed forces, after reviewing their requirements, will mobilize only up to 35,000 most of them, about 13,000, from the Air Force.
The reserve forces will be used in what is called "homeland defense" that is, security duties in the United States itself. The emphasis on Air Force reservists reflects the requirement for stepped up air patrols following Tuesday's multiple aircraft hijackings by suicide terrorists.
The partial mobilization is the first since the 1991 Gulf War.