WASHINGTON — Foreign smugglers are trying to ship advanced American technologies — which can be used for weapons and spy equipment — to China, Russia and other adversaries at rates that outpace shadowy and illegal exports during the Cold War, according to United States officials and experts.

In one recent case, a Texas businessman was paid $1.5 million to buy special radiation-resistant circuits for space programs in Russia and China. The businessman, Peter A. Zuccarelli, was working with a smuggling ring run by a Pakistani-born American citizen; court documents show Mr. Zuccarelli created fake shipping documents and mislabeled the circuits as parts for touch-screen computers. He was sentenced in January to four years in prison.

In another case, the Chinese citizen Fuyi Sun sought to buy M60 carbon fiber, which is used in military drones, from undercover federal agents at Homeland Security Investigations. Using the word “banana” as code for “carbon fiber,” Mr. Sun took steps to conceal and export $25,000 worth of the material that he bought shortly before he was arrested. He was sentenced in September to three years in prison.

“He openly claimed in an email that he was closely associated with the military,” said Pete Gizas, a special agent with Homeland Security Investigations, a branch of Immigration and Customs Enforcement.