Former Los Alamos physicist Wen Ho Lee pleaded not guilty yesterday to charges that he mishandled a vast quantity of nuclear secrets, and a federal magistrate in New Mexico ordered him to remain in custody without bail.

After a daylong hearing in Albuquerque, U.S. Magistrate Don Svet said that releasing Lee pending trial would pose a "clear and present danger" to the United States. "The weight of the evidence indicates to me that I'm required to order his detention, which I'm going to do," Svet said, according to the Associated Press.

Lee, a 59-year-old, Taiwan-born U.S. citizen who worked for almost 20 years at Los Alamos National Laboratory, was arrested last Friday on a 59-count indictment that accused him of endangering national security by downloading nuclear secrets from Los Alamos's computer system to cassette tapes and then taking them from secured areas of the lab. The indictment said seven of the 10 cassettes were missing.

At the hearing, federal prosecutor Robert Gorenceos argued that Lee, who has been under 24-hour FBI surveillance for more than a year, should be kept in jail because he posed "a substantial risk of flight."

Defense lawyers said the seven tapes were destroyed but did not elaborate on how, when or by whom.

"There's no evidence he has the tapes, disclosed the tapes, attempted to disclose the tapes. Is there any evidence in this huge investigation [of attempted disclosure]? The answer is no," one of Lee's attorneys said, according to the AP.

The physicist's wife, Sylvia Lee, who also had worked at the laboratory in an administrative job, and their daughter, Alberta Lee, attended the hearing. Alberta Lee said her father was innocent. "My family and I love my father and will continue to support him and stand by him," she told reporters.

Lee's indictment and arrest came after a four-year investigation into alleged Chinese espionage at the U.S. nuclear weapons laboratory. Lee has been the prime suspect since 1995, but no evidence has turned up that he passed any material to the Chinese.

Lee has steadfastly denied being a spy. He was fired from Los Alamos in March after he failed a polygraph and was found to have committed security violations. After his firing, a search of his office and desktop computer showed he had downloaded the secret files.

Yesterday's hearing provided the most detailed description yet of the importance of the material Lee downloaded in 1993, 1994 and 1997.

Stephen Younger, director of nuclear weapons programs at Los Alamos, testified that the classified data and computer codes that Lee had removed could reveal the complete design of current U.S. nuclear weapons. These files "represent centuries of work," Younger said, adding that although the downloaded computer programs could be used for purposes other than weapons design, that would be "like using a Ferrari to haul cement."

In an interview broadcast earlier this year by the CBS news program "60 Minutes," Lee said he downloaded the material from Los Alamos's secure computer system to his unsecured workstation because it made it easier to work with, and he suggested that other scientists did the same thing. He did not mention putting any data on cassettes or taking them out of his secure work area.

Lee was not accused in the indictment of turning the cassettes over to China or any other foreign country. About half the counts came under previously unused provisions of the Atomic Energy Act, which carries a maximum penalty of life in prison for tampering with or illegal possession of nuclear secrets. The act requires the government to prove that Lee intended "to injure the United States" and help "any foreign nation."

Normally in espionage cases in which there is no direct evidence that an individual turned material over to a foreign agent, the government makes its case by showing clandestine meetings, use of hiding places, secret transfers of money, or the like. No such acts are alleged in Lee's indictment.

Instead, the government charges that Lee, by removing secret material from a secure location, could "reasonably" have expected its unauthorized disclosure, which in turn would seriously harm the security of the United States.

Asian American groups have accused the government of "racial profiling" in the espionage investigation and, along with Lee's family, have opened a legal defense fund for him.

Energy Secretary Bill Richardson, concerned about such allegations, repeated yesterday that he has "zero tolerance" for racial profiling, meaning the practice of singling out suspects on the basis of race or ethnicity.

CAPTION: Physicist Wen Ho Lee, right, is led away by an unidentified FBI agent after being arrested at his home in White Rock, N.M., last Friday.