WASHINGTON — President Trump moved forward with his planned United States Space Force on Tuesday, signing an order to begin the process for establishing a new branch of the military that would be dedicated to handling threats in space.

Mr. Trump’s directive orders the Defense Department to “marshal its space resources to deter and counter threats in space” — which the Pentagon already does. The newly created Space Force would be overseen by the Air Force, a concession to congressional critics who say the Pentagon does not need to add to its sprawling bureaucracy.

The president needs congressional approval to create a Space Force; his initial proposal for it to be a separate branch of the military — equal to the Army, the Navy and the Air Force — was met with resistance. Congress and the Pentagon recommended that the force be placed under the Air Force’s purview.

Proponents of a Space Force argue that the Air Force does not pay enough attention to outer space, even as Russia and China are developing antisatellite weapons that could pose a threat to American satellites.