A top FBI counterintelligence agent gave a suspected Chinese spy access to voluminous amounts of classified information during an alleged 20-year affair between the two, according to documents unsealed in U.S. District Court in Los Angeles yesterday.

James J. "J.J." Smith, 59, and Katrina M. Leung were arrested yesterday and charged with espionage-related offenses as the latest in a series of spy scandals rocked the FBI with allegations of betrayal, sexual intrigue and political connections.

Federal prosecutors alleged that Leung, 49, a bookstore owner and well-known contributor to the Republican Party, acted as a "double agent" during her long-running sexual affair with Smith, 59, a senior FBI counterintelligence agent who had recruited her to spy on the People's Republic of China and was acting as her FBI contact. Smith retired in 2000, after 30 years with the FBI.

The two were arrested at their homes yesterday morning in connection with the alleged theft and transfer of a single classified national defense document to the communist Chinese government. Authorities said additional charges may follow.

According to an FBI affidavit, "Smith routinely debriefed Leung at her residence and on occasion took classified documents there and left them unattended. Leung surreptitiously photocopied some of them, and documents she obtained in this manner have been recovered from her residence."

The FBI paid Leung, code-named "Parlor Maid," $1.7 million over 20 years to provide the U.S. government with information about the People's Republic of China, sources said. Officials declined comment on what information Leung provided on China, but said she passed on to Chinese officials information about FBI personnel, a telephone list from an espionage investigation and intelligence on the whereabouts of Chinese fugitives.

Investigators allege that Leung also had an intermittent sexual affair with another FBI counterintelligence agent in San Francisco. The second agent, who is not named but ran the San Francisco counterterrorism squad, allegedly warned Smith of Leung's duplicity in 1991. But Smith did not end his alleged relationship with Leung or report her to his superiors, officials said in court documents.

The San Francisco agent admitted that he continued his relationship with Leung until 1999, the documents show.

Leung was charged with obtaining classified documents with the purpose of aiding a foreign power, while Smith was charged with gross negligence for allowing her to obtain them. Both charges carry a maximum penalty of 10 years in prison. Smith was released last night on $250,000 bond, but Leung remained in custody.

The charges follow the 2001 conviction of admitted spy Robert P. Hanssen, the former senior FBI counterintelligence agent who was convicted of providing U.S. secrets to Moscow over two decades and is serving a sentence of life in prison without parole. It also is another blow to the bureau's Chinese counterintelligence program, which was widely condemned after the bungled investigation of former Los Alamos nuclear scientist Wen Ho Lee.

But the case is perhaps most reminiscent of the prosecution of Los Angeles FBI agent Richard W. Miller, who was convicted of espionage charges in 1990 for allegedly passing information to Moscow through his lover.

The FBI said Director Robert S. Mueller III learned of the allegations against Smith in January 2002, and immediately assigned Randy Bellows, a prominent espionage prosecutor, to review the case. Bellows recommended that the probe be handled by a special task force, which Mueller formed in February 2002 under FBI inspector Les Wiser.

The task force is reviewing all FBI "assets," or human intelligence sources, and the Justice Department inspector general's office has been asked to review FBI intelligence efforts, officials said.

"It is a sad day for the FBI," Mueller said in a statement yesterday. "James Smith was once a special agent, sworn to uphold the rule of law and the high ethical standards of the FBI. . . . Agent Smith not only betrayed the trust the FBI placed in him, he betrayed the American people he was sworn to protect."

U.S. Attorney Debra Yang indicated that more charges may be filed against both Leung and Smith. "There was a lot more activity spanning . . . two decades," she said at a news conference in Los Angeles.

Sources said yesterday that the Smith case was the reason that Mueller in January 2002 abruptly transferred Sheila Horan, then acting head of the national security division, which handles espionage cases. Mueller was furious that he had not been notified of the allegations earlier and abruptly transferred Horan to an administrative post as a result, the sources said.

In the late 1990s, Smith served as the FBI contact or "handler" for Johnny Chung, the Chinese American businessman who was central to the Democratic fundraising scandal that plagued the Clinton administration. Smith has hired the same defense attorney, Brian Sun, who represented Chung.

Sun declined to comment in detail on the case against his client, but said he was "very disappointed that the government chose to bring charges in this case. J.J. was a dedicated and well-respected special agent."

Fluent in English, Mandarin and Cantonese, Leung arranged numerous events for the Chinese consulate, including a 1997 banquet for 1,000 people when Chinese President Jiang Zemin stopped in Los Angeles during an official U.S. visit.

Leung and her husband contributed $27,000 to the Republican Party in the past decade, according to campaign finance documents. Leung also was well-known in Los Angeles political circles for her close ties to the leadership of the People's Republic of China, according to news reports.

One senior law enforcement official said investigators were examining the sources of Leung's political contributions.

A statement issued by Leung's two attorneys, Janet I. Levine and John D. Vandevelde, said she is "a loyal American citizen" who repeatedly put herself in danger to help the FBI, and would be vindicated.

The document at the heart of the case is a copy of a June 12, 1997, FBI memorandum found in Leung's home concerning Chinese fugitives that also "discussed reporting of national defense information by a confidential FBI source," the Justice Department said.

But investigators seized other sensitive materials found during consensual searches of her home, including a transcript of telephone conversations between Leung, whose Chinese government code name was "Luo," and a Chinese official, whose name was "Mao," court documents said.

During interviews with the FBI, Leung admitted to copying documents from Smith's briefcase, but said he did not know she was doing so, investigators said. She also said, however, that he would allow her to review documents without copying them.

Smith acknowledged in interviews with the FBI that he had "probably told Leung too much" in the course of operating her as an intelligence asset.

According to two affidavits totaling 60 pages, Smith and Leung have been secretly monitored since last summer as part of a foreign counterintelligence investigation that included the use of wiretaps, physical surveillance and clandestine searches.

Edds reported from Los Angeles. Staff writers Dana Priest and Susan Schmidt contributed to this report.