Ronald W. Pelton, a former National Security Agency employe who went on trial here today on espionage charges, was described by prosecutors as a compendium of information about secret communications intelligence from the Soviet Union, including a previously undisclosed U.S. capability to intercept "command and control" communications from "the highest level in the Soviet Union."

A prosecutor outlining the case against Pelton said one program he betrayed involved an "upgraded capability" to collect and process intercepted Soviet messages. A senior NSA official testified today that this system -- not yet operational when Pelton left the agency in 1979 -- is now an "ongoing operation" that is planned for use into the 1990s.

Even Pelton's court-appointed attorney seemed surprised by this revelation from the NSA official on the witness stand, and noted that Pelton himself could not have told the Soviets that the advanced processing system had been deployed.

Pelton, described as a former middle-management staff officer in NSA's Soviet communications unit, wrote what the prosecution termed a 60-page "encyclopedia" on Soviet communications intelligence in 1978, and subsequently sold the information in it to the Soviet Union, according to the government case presented today. That document, called the Signal Parameters File, told the Soviets which of their communications signals were being given top priority by the United States, and how quickly they were being analyzed, according to prosecutor John Douglass.

Douglass outlined five top secret NSA projects, in addition to the Signal Parameters File, that the government contends Pelton gave to the Soviets. One of them, referred to in court today only as "Project E," concerned a particular Soviet signal that carried "command and control information from the highest level in the Soviet Union to the next highest level," according to Donald R. Bacon, Pelton's former supervisor at NSA.

Another project Pelton allegedly told the Soviets about, "Project B," concerned "the upgrading of the actual equipment that collects Soviet signals . . . and involved equipment to be used years and years into the future," Douglass said.

That project, according to Bacon, "is ongoing" even now. It was planned, he said, by an NSA committee that included Pelton and was launched sometime after his departure from the agency in 1979.

Bacon and Douglass said that Pelton's knowledge of the project included details on how quickly Soviet signals information could be forwarded to NSA and how it would be processed.

Douglass told the jury that the highly secret NSA is in the business of collecting and intercepting radio, microwave and cable communications links that contain military information, including movements of troops and ships, and the development and uses of weapons systems. Some of that information, he said, is "in plain text, some in cipher or code, some in weapons data."

"Our ability to know what's going on in a foreign military organization," Douglass said, "is one of the most significant means this nation has to protect itself." If the Soviet Union knows which of its signals the United States is able to intercept and decode, he said, it can change its communications methods to prevent the United States from further eavesdropping and intelligence gathering activities.

Douglass said the actual code names of the projects Pelton allegedly sold to the Soviets will not be mentioned at trial, nor will specific details about the projects, including the time and place of collection of information.

He said the government has an interest in continuing to keep that information secret because other "unfriendly" nations besides the Soviet Union "have a very keen interest in the same kind of information."

Douglass said Pelton began his alleged relationship with Soviet agents by going to the Soviet Embassy in Washington on Jan. 15, 1980, after contacting Soviet officials by telephone the day before. Edited transcripts of two phone calls Pelton allegedly had with Soviet officials on Jan. 14 and 15, 1980, were released today. They were obtained through wiretaps.

At the embassy, Douglass said, Pelton told the Soviets of the location of "Project A," later described by government witness Hubert Atwater as "a set of equipment set up to collect signals off a particular Soviet communications link."

Pelton "took a map and took his finger and showed the Soviets where it was," Douglass said.

He said the Soviets, while not able to identify the precise location of the equipment, were able to figure out what "communications link" it was drawing information from.

The place that Pelton pointed to on the map, according to informed sources, was the Sea of Okhotsk between the Kamchatka Peninsula and the eastern Soviet coastline.

Atwater, a senior signals conversion officer at NSA, testified that he worked directly with Pelton during the mid-1970s.

He said that Project A, like the other projects Pelton is alleged to have divulged to the Soviets, was classified top secret, and was accessible to people cleared for that level of information only on a "need to know" basis.

Projects C and D, which prosecutors also allege Pelton told the Soviets about, involve the locations of two special collection projects, according to the government.

Pelton, who earned $24,500 annually while at NSA, is not accused of delivering any classified materials to the Soviets. But Douglass and Pelton's two former NSA colleagues described him as a highly intelligent man with an extraordinary ability to recall technical information.

"He could retain information for many years," said Bacon, and for that reason was often consulted by his superiors when they needed to know the history of various NSA activities.

When Pelton left NSA in 1979, Douglass told the jury, "he didn't go home with stacks of classified documents -- what he had was in his head." Pelton is accused of allowing the Soviets to "pick his brain" during lengthy debriefing sessions.

Pelton is accused of participating in two such sessions at the Soviet Embassy compound in Vienna, sessions that lasted three to four days each in which he provided written answers to written questions.

Pelton, who joined NSA in 1965, worked in a "hands on" capacity in the collection of communications intelligence until 1973, Douglass said.

From then until 1979 he moved up from a "line" job to a "staff organization" job, which gave him access to "a tremendously broad range of information" about Soviet communications intelligence.

When he left the agency shortly after declaring bankruptcy in 1979, Douglass said, he was a prime candidate for selling out to a foreign power: "He was in a desperate financial situation and he had a gold mine of information."

Pelton's court appointed lawyer, Fred Warren Bennett, said in his opening statements to the jury that he believes the case should hinge not simply on what Pelton did or did not tell the Soviets, but on how the government obtained statements on Nov. 24 that resulted in his arrest that night on espionage charges.

"This case is also about civil rights and civil liberties, about law enforcement interviewing techniques," said Bennett. He said he intends to show that the jury should refuse to consider statements Pelton made to two FBI agents as evidence because the statements were not freely given.

The agents, Bennett said, made implied threats to Pelton, failed to advise him of his rights, and made false promises in order to get information from him.

"Without his statements," said Bennett, "the evidence will be insufficient to convict and the government's case will crumble like a house of cards."

Douglass said that after meeting with the Soviets at their embassy in 1980, Pelton kept in contact with them through prearranged clandestine phone calls he received on a wall phone at the Pizza Castle in Falls Church.

Prior to his trip to Austria in late 1980, Douglass said, Pelton got a call from a Soviet agent on the Pizza Castle phone and was told to go to a phone booth at another location. There he allegedly found $2,000 in expense money hidden in a magnetic container.

He then flew to Vienna as instructed, and strolled around a public garden in the city, where he was approached by Soviet agents and escorted to the embassy compound. He received $20,000 for information provided during that trip, Douglass said, and $15,000 for a trip with a nearly identical scenario in 1983.

Pelton made a third trip in April 1985, but never connected with Soviet agents, according to Douglass, because he had lost about 75 pounds and they did not recognize him.

Pelton had planned to make another trip in October 1985, Douglass said, but ran out of gas on his way to the Pizza Castle from Annapolis and missed the phone call from Soviet agents.