Pentagon defining homeland security role. (Security Beat).

The Defense Department continues to focus and clarify its role in homeland security, said Peter Verga, special assistant to the secretary of defense for homeland security. The department contributes to homeland security in two ways, he said. "First, we guard against threats and aggression, and we provide support for civil authorities," he said. The Defense Department "effectively bridges the divide between homeland security and national security," said Verga.

Speaking at a conference of the American Institute of Aeronautics and Astronautics, Verga said that the Defense Department has a history of involvement in domestic security matters, providing civil support to communities in three ways. First, in extraordinary circumstances, there has been a need for the deployment of Defense Department air combat power in the continental United States. Second, in emergency circumstances, the Defense Department has assisted a lead federal agency, such as the Federal Emergency Management Agency (FEMA), by providing military resources for projects, such as an environmental or hazardous material clean-up.

Verga said the Defense Department most recently partnered with FEMA (one of 22 agencies absorbed into the Department of Homeland Security), to pick up the scattered pieces of the Space Shuttle Columbia in Texas and Louisiana.

Third, the Defense Department provides support and assistance to states or localities for temporary security situations, when the resources of the department are made available to a lead federal agency.