Magistrate Judge Deborah Robinson decided there was too much of a flight risk for Stewart Nozette, 52, of Chevy Chase, Md., to be free while he awaits trial.

Nozette, arrested last week, pleaded not guilty to charges of attempted espionage. He is accused of seeking $2 million for selling secrets to an undercover FBI agent posing as an Israeli intelligence officer.

Nozette had high-level security clearances during decades of government work on science and space projects. He was known primarily as a defense technologist who had worked on the Reagan-era "Star Wars" missile-shield effort.

Because he knows so many secrets, Attorney General Eric H. Holder Jr. has ordered special communications restrictions placed on him while he is in jail, authorities said.

"He is now a treasure trove of some of our most sensitive matters," prosecutor Anthony Asuncion said.

During the hearing, Asuncion played video excerpts of an undercover sting operation in which the scientist lounges on a hotel-room couch, discussing the possibility of having to flee the country if he comes under scrutiny from U.S. officials.

Nozette looked starkly different as he sat in court yesterday. Wearing baggy, black-and-white-striped jail clothes, he stared passively as the screen showed him eating and laughing with the undercover agent.

Asuncion said Nozette told the agent he had passed classified information to Israel in the past. Nozette is not charged with doing so.

His lawyer, John Kiyonaga, said there was no basis for that accusation and noted that the government's charges did not include it. He also said the video recordings left out significant parts of a longer conversation.

According to prosecutors, Nozette was paid $225,000 by a company wholly owned by the Israeli government and regularly spoke to its officials. In court, Kiyonaga identified the company as Israel Aircraft Industries.

During one of his secretly recorded conversations with the undercover FBI agent posing as an Israeli agent, Nozette said: "I thought I was working for you already. I mean, that's what I always thought. . . . [The foreign company] was just a front."