The concern about anti-satellite weaponry from Russia and China is a real one, Defense Department officials and aerospace experts say. A United States intelligence threat assessment warned in February that Russia and China would be able to shoot down American satellites in two to three years, potentially endangering GPS satellites as well as military and civilian communications satellites and the country’s spy satellites.

The satellites help guide aircraft carriers in the Persian Gulf, drones in the skies above Yemen and fighter jets over Syria. American ground troops on patrol in Afghanistan use GPS coordinates to track their movements, and intelligence officers at C.I.A. headquarters in Langley, Va., depend on spy satellites to gather information on adversaries.

“Everything the U.S. military does today relies on space,” said Brian Weeden, the director of program planning at the Secure World Foundation, a nongovernmental organization that studies space policy. Take drones, for instance, he said. “Their signals are routed over satellites. Data is routed over satellites. Intelligence satellites do the B.D.A. after strikes,” he added, referring to battle damage assessments the military makes to determine whether targets have been destroyed.

In the early 1990s, after the fall of the Soviet Union, the American military exercised restraint on anti-satellite weaponry, Mr. Weeden said, in the hopes that two other so-called great powers — Russia and China — would follow suit. But “great power adversaries have not decided to exercise the same restraint,” he said.

Now Russia and China are getting close to developing ways to disable American satellites, and if the United States goes to war with either of those countries, the fear is that they could interfere with American communications.