SANTA ANA, Calif. — The prosecution wasted no time Thursday in challenging the credibility of an accused Chinese spy, Chi Mak, who has denied he was trying to aid the Chinese government when he arranged to send disks containing submarine propulsion technology to China.

“You’re a liar, aren’t you?” a prosecutor, Gregory Staples, said as he opened his 90-minute cross-examination of the defendant.

“No,” Mr. Mak said calmly.

Mr. Staples went on to suggest that Mr. Mak, an electrical engineer who worked for a Navy contractor, Power Paragon, lied repeatedly after his arrest in October 2005, as well as on an immigration form and an application for a security clearance to handle classified information.

Mr. Mak conceded that he lied to the FBI and a Navy investigator about how often he had traveled to China, but he said his answers to other questions were simply “not complete.” For instance, Mr. Mak now maintains that the disks were intended for two academics in Hong Kong and a family friend in mainland China. However, at his initial interrogation, he mentioned only one of the Hong Kong professors.

“I still don’t believe I lied,” Mr. Mak said of the omission.

“You just admitted to almost a dozen lies you told,” the prosecutor said at one point.

Mr. Mak has said some of the misstatements came because he was scared and confused by the circumstances of his arrest. He said he was in bed when the FBI arrived at his home and he was taken out of his house initially wearing just underwear. The defense has also noted that the interrogation continued late into the night and that agents lied to Mr. Mak about what was on the disk they found when his brother and sister-in-law were arrested the same night as they prepared to board a flight to China.

“They were pushing me that night,” Mr. Mak said. He insisted yesterday that he has no idea why his brother used a program to reduce the three disks of technical information to one and placed the disk among a set devoted to learning English.

“Why would he compress it down to one disk and hide it?” Mr. Staples asked.

“I’m not aware,” Mr. Mak replied. He said he saw nothing wrong with sending the papers to China because they had been presented at public conferences attended by foreigners.

Mr. Mak said he omitted some relatives from his security clearance application because he had also left them off an immigration form he filled out years earlier. “I want to keep consistent. They have no relationship with my work,” he said.

“Once again you lied to get a benefit?” Mr. Staples said.

Mr. Mak replied that he never wanted to handle classified information, but one of his supervisors said it would benefit the company if he could work on such projects. “I’m not interested in security clearance,” he said. “I had no reason to lie.”

Mr. Staples expressed incredulity at some of Mr. Mak’s answers, but raised his voice only occasionally. The prosecutor, who is broad-shouldered and stocky, seemed to be taking care not to engender sympathy for the defense by intimidating Mr. Mak, 66, who is slight and testified that he weighs less than 140 pounds. The relatively brief cross-examination and the lack of fireworks also seemed intended to suggest to jurors that Mr. Mak’s testimony was so implausible that it should be dismissed out of hand.

Some of the most damning evidence against Mr. Mak may be notes found in his home and his brother’s home, containing what seems to be a series of coded phrases. One phrase, “send a card,” appeared next to the words “help your mother in law.” Mr. Mak testified Wednesday that he got the list from his niece who said it could be used to communicate about her ailing mother in China without upsetting people.

However, Mr. Staples pointed out that some of the entries do not seem to pertain to a sick or elderly relative. For instance, “supermarket” appears next to the phrase “good material.”

Mr. Mak said he considered the list absurd and told his niece so. “The whole thing’s ridiculous,” he said yesterday. Nevertheless, Mr. Mak conceded, he copied the list by hand and gave it to his brother.

Mr. Mak’s wife, brother, sister-in-law, and nephew have all been charged with conspiracy to illegally export defense articles. They are set to be tried later.

Mr. Mak testified that he does not think his brother is a spy. However, defense lawyers have tried to put some distance between the two men by arguing that their client had no knowledge that the disk would be encrypted and that Mr. Mak’s brother misled him about details of the couple’s travel plans on the night of the arrest.