A Northrop Corp. engineer accused of trying to sell "Stealth" bomber technology to FBI agents posing as Soviet spies was ordered held without bail today.

U.S. Magistrate Joseph Reichmann said of the engineer, Thomas Patrick Cavanagh:

"Someone that would do the acts he is alleged to have done . . . is a threat not just to this community, but to the country as a whole."

Cavanagh's attorney, federal public defender Denis Landine, had urged the judge to grant bail for the 40-year-old engineer, saying the money would come from equity in homes owned by Cavanagh's mother, his estranged wife and his girlfriend.

Landine said Cavanagh had no criminal record and no history of alcohol or drug problems.

"He is devoted to his two sons," Landine said. "He is devoted to his mother. He has other relationships that are strong. In fact, at this point it could be said that all he has are those relationships . . . . Basically it comes down to whether in all conscience he could leave his own family, and leave them without everything they've worked very hard for."

But Assistant U. S. Attorney Percy Anderson argued that "conscience is really not a word this defendant is familiar with."

Anderson contended that Cavanagh had met with FBI agents posing as Soviet officials on at least three occasions, and made at least one delivery of classified information that he had smuggled out of the Northrop facility in Pico Rivera.

Anderson said that at the time of Cavanagh's arrest he was armed with a loaded .45-caliber automatic weapon.

Reichmann said, "I just don't feel that I could come up with a set of facts and conditions that would secure the appearance of this defendant."

Cavanagh was arrested Tuesday at a hotel in the Los Angeles suburbs as he allegedly passed a briefcase that contained the Northrop documents to the undercover agents in exchange for $25,000.

The meeting was set up after the FBI said it developed information that the engineer was trying to sell national security secrets.

Justice Department sources said the documents involved the Stealth bomber, which is being designed to penetrate enemy territory without being detected by radar.

If convicted, Cavanagh could face a sentence of life in prison.

The Los Angeles Times reported yesterday that Cavanagh came to the FBI's attention through a secret "contact program" that the FBI employs to maintain close physical and electronic surveillance of Soviet diplomatic facilities in the United States.

Intelligence officials were quoted as saying that the value of this around-the-clock surveillance, which they said began shortly after World War II, is made clear by the Cavanagh case.

The contact program is reportedly one of the largest items in the FBI's classified counterintelligence budget.

Cavanagh reportedly came to the FBI's attention when, using the pseudonym of Peters, he made numerous attempts to contact Soviet officials at their consulate in San Francisco and the Soviet embassy in Washington. The Soviets reportedly did not respond to Cavanagh's offer to sell them secret information.