AN FRANCISCO, Sept. 19 — A Chinese software programmer was arrested Tuesday after a Silicon Valley company complained that he had tried to steal software used in seismic imaging of oil fields, company officials said today.

The programmer, Shan Yanming, 32, has been in the United States since the end of April as part of a contract between the state-owned China National Petroleum Corporation and 3DGeo Development., a Mountain View, Calif., software company.

Executives at the company said that the Chinese programmer, who had been training in the use of the company's software, was caught trying to use a company computer password to download company software to a portable computer last Thursday.

At the time, the company confiscated the computer and told the programmer to leave the premises and return to his apartment. He was arrested by F.B.I. and local law enforcement officials on Tuesday at the San Francisco International Airport while waiting to leave the country.

The programmer, who is in custody at the Santa Clara County Jail, has not yet been charged, according to an F.B.I. agent involved in the arrest.

"He was trying to gain access to our high-end seismic imaging software, which is proprietary," said Dmitri Bevc, president and co-founder of 3DGeo.

Silicon Valley companies have frequently been the target of both industrial and government espionage. Executives at the software development company said that they had discovered another Chinese employee from the same company trying to steal software five years ago, but had not reported the incident to the government.

As a result of the earlier incident the company was alert to the possibility of theft, he said.

"We were watching him," Dr. Bevc said. "We knew that a security risk was possible. Our engineers were watching him and they saw him start to do this."

According to the company officials, the programmer had a software tool known as crack that is used to extract passwords that have been stored and encrypted. But they said they did not believe that the program had been used successfully. Instead, they said the programmer might have observed another employee entering the password and then copied it.

3DGeo executives said they did not have any indication whether the attempted theft was sanctioned by the Chinese National Petroleum Corporation. They said the Chinese company had purchased one program from the company, but that the theft involved a more powerful software program that would typically sell for $100,000 to $200,000.

F.B.I. officials said the programmer had been assigned a public defender. Calls to the Chinese consulate in San Francisco were not returned.