The FBI (search) is reviewing each of the thousands of people who provide it intelligence to make sure they are being handled properly and giving accurate, high-quality information.

The review began last summer after FBI Director Robert Mueller learned about alleged double agent Katrina Leung (search), now charged with giving the Chinese government classified information she took from her longtime lover, retired FBI counterintelligence agent James J. Smith.

The review is being done by an intelligence division task force answering to the FBI's No. 2 official, Deputy Director Bruce Gebhardt. The work involves checking sources' information for consistency and any contradictions by comparing it with other intelligence. Lie detector tests are being used in select cases.

"Counterintelligence and counterterrorism are top priorities, and human sources are the backbone," FBI spokesman Mike Kortan said. "We're taking a top-to-bottom look at every key asset to ensure that the information we're getting is valid."

Kortan declined to say whether the investigation has uncovered any other alleged double agents or wrongdoing by FBI personnel.

A federal grand jury in Los Angeles returned a six-count indictment Wednesday charging Smith with gross negligence and wire fraud, charges that carry a maximum sentence of 40 years in prison. The government faces a Friday deadline to seek grand jury indictments against Leung as well.

Although the exact number of FBI intelligence "assets" is secret, officials say it likely numbers in the low thousands. How much money is spent also is classified, but it is easily in the millions of dollars per year.

According to court documents, the FBI paid Leung $1.7 million over nearly two decades for information about the People's Republic of China. That put her in the FBI's top echelon category, reserved for only the most valuable assets.

FBI intelligence assets, most of them operating in the United States, provide detailed information about the inner politics, movements and plans of foreign governments or organizations such as terrorist groups. They differ from informants, who also are covert but are used to build cases against drug dealers, mobsters, corporate swindlers and other mainly domestic criminals.

The review of intelligence assets is partly a response to the attacks of Sept. 11, 2001, when it became clear the FBI needed to recruit more informants for its new top priority of detecting terrorists and preventing attacks.

But it was given new urgency by the Leung case, in which Smith has been charged with gross negligence for allegedly giving her access to classified material during a sexual relationship that lasted most of two decades. The two, both of whom are married, appeared in public together, with Leung even videotaping Smith's retirement party in 2000, according to court documents.

California Rep. Jane Harman, ranking Democrat on the House Intelligence Committee (search), has been briefed on the case and said the FBI is "hugely embarrassed."

The FBI is trying to assess the damage done, including whether national security secrets were given away and U.S. investigations of Chinese spying compromised.

Further complicating the case are allegations Leung also had an affair with William Cleveland, a former FBI counterintelligence agent based in San Francisco. Cleveland has not been charged and is cooperating, officials say, but that relationship also suggests that changes are needed in the way intelligence assets are handled and monitored, officials say.

Eventually, oversight of both intelligence assets and criminal informants will fall under the new FBI Office of Intelligence at headquarters. Mueller recently named Maureen Baginski, head of signals intelligence at the eavesdropping National Security Agency, as assistant FBI director in charge of those programs.

The internal intelligence review comes as Justice Department Inspector General Glenn A. Fine is putting the finishing touches on a classified 600-page report on the case of Robert Hanssen, once a top FBI counterintelligence agent who was sentenced last spring to life in prison for spying for Russia and the former Soviet Union.

Much of the Hanssen report will remain secret, but Fine expects to release a summary to the public.

Hanssen's case produced changes at the FBI, including regular polygraph tests for counterintelligence agents and closer scrutiny into their financial backgrounds to identify weaknesses that could be exploited by foreign powers.

None of those changes was in effect while Leung allegedly was spying for China and passing on Chinese secrets to Smith. Fine also will investigate that case, although the criminal cases against Smith and Leung will begin moving forward first.

The Leung case already has led to an FBI internal review of management lapses that apparently kept Leung on the payroll despite evidence gained through an intercepted phone call in 1991 that showed she may have been passing information to Chinese intelligence agents.