A Senate panel called off hearings this week on the FBI's investigation into Chinese espionage after FBI Director Louis J. Freeh warned that the testimony could hinder the prosecution of physicist Wen Ho Lee.

Sen. Arlen Specter (R-Pa.), chairman of the special subcommittee that had planned to conduct the hearings, said Freeh objected that questions relevant to the trial could be asked at the hearing and the answers could "be subject to discovery by [Lee's] defense."

Lee was arrested by the FBI last week and pleaded not guilty Monday to charges that he mishandled nuclear secrets by downloading data from a classified computer system at Los Alamos National Laboratory in New Mexico to his desktop computer and to cassette tapes, seven of which are missing. A federal magistrate ordered him to remain in jail pending trial.

Specter said his subcommittee of the Senate Judiciary Committee still plans to hold hearings at some future date. In the meantime, he said, the subcommittee will continue to review FBI files on an investigation that began in 1996 into China's alleged theft of information about the design of the most advanced U.S. nuclear warhead, the W-88. The subcommittee already has obtained documents indicating that Lee quickly became the subject of that investigation, even though the FBI had been told that some 250 individuals has access to the same information. Lee has not been charged with passing secrets to China. But his arrest grew out of the espionage investigation; when agents searched his office computer earlier this year, they found evidence that the 59-year-old, Taiwan-born scientist had downloaded classified information and then tried to delete it.