Jury selection began Tuesday in the federal trial of a former top engineer at a major U.S. defense contractor accused of stealing military secrets for the Chinese.

Federal prosecutors have portrayed defendant Chi Mak as a foreign agent who used his position to steal some of the most advanced and closely guarded naval technology in the world, including silent-running propulsion systems that can make submarines virtually undetectable.

Defense attorneys argue that the 66-year-old is a devoted American who would never harm his adopted country.

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An initial group of about 75 jurors was brought to the courtroom Tuesday and questioned as Mak looked on. Opening statements could begin later this week for a trial U.S. District Judge Cormac Carney has said could run four to six weeks.

Mak, a U.S. citizen since 1985, is charged with conspiracy to export U.S. defense secrets to China, possession of property in aid of a foreign government and failure to register as a foreign agent. He could get more than 50 years in prison if convicted.

As a top engineer at Power Paragon, an Anaheim-based subsidiary of the nation's sixth-largest defense company, L-3 Communications, Mak helped develop some of the most advanced and closely guarded naval technology in the world, including silent-running propulsion systems that can make submarines virtually undetectable.

But prosecutors say Mak was also working for his native China from 1983 until his arrest two years ago, stealing hundreds of documents about a number of defense systems.

Mak allegedly took documents from Power Paragon, copied them to computer disks and encrypted them with the help of his brother, Tai Mak, and nephew, Billy Mak, before trying to pass them to a Chinese contact.

Tai Mak and his wife, Fuk Heung Li, were arrested in October 2005 at Los Angeles International Airport as they prepared to travel to Hong Kong and China.

Hidden in their luggage were encrypted disks containing copies of documents on a submarine propulsion system, according to court papers.

Chi Mak was arrested several days later.

According to the FBI, Chi Mak told investigators his brother was giving the information to a researcher at a Chinese university center that conducts operations research for and receives funding from the People's Liberation Army.

During a search of Chi Mak's home, investigators found restricted documents on the DDX Destroyer, an advanced technology warship, according to court papers.

They also found lists in Chinese asking Chi Mak to get documents about submarine torpedo technology, electromagnetic artillery systems, weapon standardization, early warning technology used to detect incoming missiles, and defenses used against nuclear attack, the court papers said.

Chi Mak's lawyers have said the government has grossly exaggerated the evidence against their client, and he would never do anything to harm his adopted country.

"Every person you turn to says he's the most generous, committed engineer in the company," Mak attorney Ronald Kaye said recently. "My client is committed to discussing and learning about technology — that's all."

Tai Mak, Li, Billy Mak and Rebecca Laiwah Chiu, the wife of Chi Mak, have all pleaded not guilty and await trial.