SAN FRANCISCO — With little fanfare, one of the most significant Chinese espionage trials in years is set to get under way next week in a Southern California courtroom.

A senior engineer for a company with numerous American Navy contracts, Chi Mak, 66, is charged with attempting to smuggle designs for quiet submarines to China and with acting as an unregistered agent of China in America. Four other members of Mr. Mak’s family face similar charges and are expected to be tried separately at a later date.

The alleged ring was broken up in 2005 when agents intercepted two of the family members at Los Angeles airport preparing to board a flight to Hong Kong. According to the government, hidden in their carry-on bag, in a package of CDs for learning English, was a disk containing sensitive, encrypted data on quiet propulsion systems for submarines.

Mr. Mak, a naturalized American citizen born in China, has pleaded not guilty. “My client’s character is absolutely unblemished,” a defense attorney, Ronald Kaye, said.

A lawmaker who is following the prosecution said he believes it addresses only a small part of a far-ranging intelligence gathering effort by Beijing. “So much of what happens with China goes on under the radar screen. It is not just this case,” Rep. J. Randy Forbes, a Republican of Virginia, said.

A spokesman for the Office of the Counterintelligence Executive, Ross Feinstein, said China is considered one to have one of the world’s most active espionage programs, along with Russia, Iran, and Cuba. “China is at the top of our concerns,” Mr. Feinstein said.

One of the unusual aspects of Mr. Mak’s case is that he is not charged with espionage as such. In addition, the government has not alleged that the designs on the disk seized at the airport were classified. Instead, prosecutors claim that the data involve the kind of weapons-related technology that requires an export license, something Mr. Mak never sought.

Mr. Kaye said the government made little effort to safeguard the material. “As you can see in the pleadings … every document in this case was distributed at a public conference,” the attorney said.

Material in the public domain is usually exempt from export controls, but the government argued that an embargo imposed on China after the Tiananmen Square massacre in 1989 made it illegal to share even widely disseminated defense materials with Beijing.

Defense lawyers have argued that the “munitions list” the government contends the submarine-related designs were on is vague and subject to interpretation. After Mr. Mak and his family members were arrested, the government obtained certifications from the State Department that the data were covered, but Mr. Kaye asserted that it is unfair to hold his client criminally responsible because of a determination made after he was arrested. The defense attorney also noted in court filings that Mr. Mak’s employer, Power Paragon, concluded that one of designs was not subject to export controls.

Judge Cormac Carney, who will oversee the trial, ruled that the State Department determinations are binding. However, to get a guilty verdict, the prosecution will be required to show that Mr. Mak knew that he was breaking the law by attempting to send the data to China.

Jurors are expected to see excerpts from audio and video surveillance of the suspects, including a camera placed over Mr. Mak’s dining room table. After a defense request, the government has agreed not to play for jurors certain inflammatory statements Mr. Mak allegedly made on the tapes, including claims that America brought terrorist strikes on itself and that North Korea has the right to develop nuclear weapons.

Judge Carney has ruled that jurors may hear that, decades ago, Mr. Mak recorded the comings and goings of American warships in Hong Kong harbor in a logbook he kept. Jurors also may hear about torn-up notes allegedly found in Mr. Mak’s home that prosecutors contend are a Chinese government shopping list for information on missile defense, artillery, and torpedo systems. The prosecution also may play a recording suggesting that Mr. Mak was part of “the red flower of North America,” a term prosecutors claim is code for a Chinese intelligence operation.

In a move that could trigger a First Amendment battle, prosecutors have indicated that they plan to close a portion of the trial to the press and public. In a filing earlier this week, the prosecution said it plans to clear spectators from the Santa Ana, Calif., courtroom when a “classified booklet” related to the case is introduced into evidence. There is no indication in the brief whether the judge has approved this technique or whether jurors made privy to the information would be prevented from discussing it once the trial concludes.

Potential jurors were in court earlier this week to fill out a questionnaire. Jury selection is expected to get under way in earnest on Tuesday, with opening arguments likely that day or the next. A spokesman for the prosecution, Thomas Mrozek, said he could not comment because his office considers the trial to be in progress.

Mr. Forbes said he is not surprised at the allegations in the California case because China’s interest in submarine technology is particularly acute. “Within a few years, they’re actually going to have more subs than the United States will have,” he said.

The congressman said he worries that the focus by the press and policy-makers on other national security issues is diverting attention from China’s long-term efforts in America. “Iraq has got the headlines today, but you mark this down: Five years from now, we’re not going to be talking about Iraq, we’re going to be talking about China,” he said.