ALEXANDRIA, Va. (AP) _ A civilian computer expert working for naval intelligence was accused Wednesday of passing at least 50 intelligence documents to a South Korean agent. American officials were scrambling to determine the scope of the security breach.

Robert Chaegon Kim, 56, was ordered held without bail at least until Monday, when a pre-trial detention hearing is scheduled in U.S. District Court here, a few miles from the nation's capital.

In a 20-page affidavit, the FBI said it has evidence that Kim, who worked for the Office of Naval Intelligence, passed dozens of classified records to Baek Dong-Il, a South Korean navy officer, during a five-month span earlier this year. Officials have not discovered any evidence Kim was paid for his efforts, a senior law enforcement official said.

``We think we know what he did and how much damage was done,'' said a Pentagon official, who spoke on condition of anonymity. ``Is it serious? Yes. Will the national security of the nation fall? No, I don't think so.''

A video camera secretly installed in Kim's office taped him copying and printing classified records on his computer, the FBI affidavit said. Searches of his mail revealed that he was sending them to Baek, who works at his nation's Washington embassy, and telephone wiretaps indicated the two discussed the deliveries, the affidavit said.

If convicted of transmitting classified information to a foreign agent, Kim could face a maximum penalty of 10 years in prison. But prosecutors were contemplating bringing espionage charges that could carry a life sentence, said a law enforcement source who spoke only on condition of anonymity.

The Clinton administration reacted angrily to the incident even though it was a carried out by an ally with which the United States has a security treaty. The United States not to share all of its secrets, even with its closest allies.

In recent years, the most famous incident involving spying by a friendly country occurred when Jonathan Pollard, a Navy intelligence analyst, was caught passing state secrets to Israel and was sentenced to life in prison.

State Department spokesman Glyn Davies said the senior South Korean diplomat in Washington was summoned to the department Wednesday and was told the United States ``is very disturbed at this development.''

But White House Press Secretary Mike McCurry tried to play down the potential international implications of the arrest. He said U.S.-South Korean relations ``are strong and of the nature that they can endure any alleged wrongdoing by an individual.''

The South Korean Embassy said it would have no immediate comment.

Kim, a Seoul native, became a U.S. citizen in 1974. He began working for the Office of Naval Intelligence in 1978 and gained a ``Top Secret'' security clearance a year later, court papers said.

He worked on a computer system that gave him access to top-secret documents generated by other U.S. intelligence-gathering agencies, the affidavit said. The Pentagon official said the system also included information considered ``above top secret.''

``Kim regularly searches the system to find classified documents relating to military, political and intelligence matters in the Asia-Pacific region,'' the affidavit stated. ``Kim copies and stores these documents in his work computer, removes classification markings, prints them on his office printer, and transmits them to Baek Dong-Il.''

The Pentagon official said an assessment to determine the damage done by Kim won't be completed until investigators review materials seized from his home, which FBI agents raided late Tuesday night.

The affidavit offered few specifics about the nature of the documents Kim was passing. However, the case summary noted that the first batch of 10 documents Kim is accused of passing to Baek included top secret records pertaining to North Korea.

Kim also worked on a maritime tracking computer system like one that the U.S. was trying to sell to South Korea.

In recent years, South Korea has been working harder to develop its own military technology and buy less sophisticated equipment from the United States. It also has been buying more from other countries, including Russia.

Baek arrived in the United States on Oct. 1, 1994, to begin a three-year stint as a naval attache to the South Korean Embassy in Washington.

The case against Kim began to move forward about May 5, 1996, when the FBI conducted a court-authorized search of his work computer.

On it was found a Jan. 24, 1996, letter from Kim to Baek in which Kim ``offered his services to Baek,'' the affidavit stated.

After the first set of 10 documents were transmitted until Sept. 9, Kim was seen copying and either mailing or faxing at least 50 additional documents, many of which had high-level security classifications.

Law enforcement officials have not yet developed evidence that Kim was given a shopping list of secrets sought by South Korea. The affidavit, however, did note that Kim was observed playing golf with Baek and two senior South Korean military officials at Fort Meade, Md.

Kim was employed by same Navy intelligence center in Suitland, Md., that employed Pollard, a former civilian Navy intelligence analyst now serving a life prison term for spying for Israel.

Kim's next-door neighbor in suburban Sterling, Va., Adrienne Mizell, described Kim and his wife as ``good neighbors, wonderful family.'' Kim is often seen walking his dog in the quiet neighborhood, Mizell said.