The United States lost an entire spy network, apparently in Central America, during the last 18 months after a young military sergeant attached to the National Security Agency sold top-secret intelligence data to foreign agents, Sen. Joe Biden (D-Del.) said Wednesday night.

Biden, who is a member of the Senate Select Committee on Intelligence and head of its subcommittee on secrecy and disclosure, told a student audience at Stanford University that "damage assessment reports" from intelligence agencies showed the sergeant was promoted and given an honorable discharge after selling "entire neels of this information . . . to the secret police [of a foreign government], blowing all our cover in a whole area of the world."

The Delaware senator told his audience that the incident was just one of between 40 and 60 "serious breaches of national security ranging from outright murder to major espionage" involving U.S. security agencies, according to a study of the agencies' reports. None of the incidents was prosecuted in the courts, he said, because the agencies feared such prosecution would only reveal additional sensitive intelligence information.

Biden could not be reached for comment yesterday. But other knowledgeable sources said he was referring in the Stanford speech to the specific case of a U.S. Army Sergeant who was reported last fall to have sold tapes and transcripts of U.S. bugging operations - including those involving the Panama Canal treaty negotiations in 1974 and 1975 - to Panamanian leader Omar Torrijos.

It was reported at the time that although military intelligence officials knew Torrijos paid the sergeant about $1,000 monthly through 1975 and 1976 the Army decided not to prosecute the man for fear the details o the operation would have to be revealed in open court. Instead, the sergeant was promoted and honorably discharged.

Biden said Wednesday that it would have been necessary to establish that the bugging tapes were stolen. "We would have to bring to court the man or woman who establishes they moved from his possession to the possession of the foreign government," Biden said.

"That person, in this case, happens to be an American spy in the other intelligence agency." said Biden. To produce the spy, he said, "you do one of two things: assure that person gets killed, practically speaking - and it isn't Alice in Wonderland, it's the real world out there - or we lose the ability of that deep agent."

The contents of Biden's remarks, which were part of an informal speech to Stanford students at the university in Palo Alto, Calif., were made available yesterday by the university. A Stanford spokesman said the speech was taped by a member of the university's news department.

Spokesmen for both NSA and the Central Itelligence Agency declined to comment yesterday on Biden's remarks. An official of the Senate subcommittee on intelligence leaks, a unti of the Senate Ethics Committee which has been quietly investigating the Panama bugging and NSA leaks, also refused to make any comment on the speech.

In addition to the NSA case, Biden said some of the other security breaches he had seen in the "damage assessment reports" by intelligence agencies ranked on the level of the case of Julius and Ethel Rosenberg, who were executed for stealing nuclear secrets and giving them to the Soviet Union.

Biden said he had found a lesson in the damage assessments and the lack of prosecution for those involved in security leaks. "If you're going to engage in espionage against this country," he said, "Be sure that it really does jeopardize American society."