Prosecutors say it is difficult to prove links to a foreign government, but intelligence officials say China, Russia and Iran are among the countries pushing hardest to obtain the latest technologies.

“In the new global economy, our businesses are increasingly targets for theft,” said Lanny A. Breuer, the assistant attorney general in charge of the Justice Department’s criminal division. “In order to stay a leader in innovation, we’ve got to protect these trade secrets.”

Mr. Huang, 45, who says he is not guilty, is being prosecuted under an economic espionage provision in use for only the seventh time. Created by Congress in 1996 to address a shift toward industrial spying after the cold war, the law makes it a crime to steal business trade secrets, like software code and laboratory breakthroughs. The crime rises to espionage if the thefts are carried out to help a foreign government.

Economic espionage charges are also pending against Jin Hanjuan, a software engineer for Motorola, who was arrested with a laptop full of company documents while boarding a plane for China, prosecutors said. Over the last year, other charges involving the theft of trade secrets  a charge less serious than espionage  have been filed against former engineers from General Motors and Ford who had business ties to China. And scientists at the DuPont Company and Valspar, a Minnesota paint company, recently pleaded guilty to stealing their employer’s secrets after taking jobs in China.

In two past espionage cases involving American computer companies, defendants said they saw a chance to make money and acted on their own, knowing that the information would be valuable to Chinese companies or agencies. In several cases, Chinese government agencies or scientific institutes provided money to start businesses or research to develop the ideas; that financing is what gave rise to the espionage charges.