Suspected spy Ronald W. Pelton was off by several hundred miles when he allegedly showed FBI agents the location on a map of highly sensitive U.S. intelligence-gathering equipment that he is accused of revealing to Soviet agents, according to a senior U.S. intelligence official testifying in federal court here today.

William P. Crowell Jr., chief of the Soviet communications intelligence division at the National Security Agency, said that although Pelton may have given the Soviets an erroneous location for NSA eavesdropping equipment, his disclosure, nevertheless, could have damaged national security.

Crowell said that in pointing out the general location of the equipment, Pelton had to have given the Soviets some description of the interception project. And, he said, even with the wrong location, the Soviets would have been able to deduce the general area and analyze their communications links to determine if any had been tampered with or compromised.

The map, the single piece of evidence placed under a court seal in the four-day-old trial, represents an important element in the government's case against Pelton, which is based largely on his confession to FBI agents last Nov. 24. Pelton's attorney has tried to block the government from using the confession as evidence, arguing that Pelton's constitutional rights were violated when FBI agents interrogated him before his arrest without allowing him to have a lawyer present.

An FBI counterintelligence officer testified Wednesday that near the end of a five-hour interrogation session last November, Pelton recounted how he walked into the Soviet Embassy in Washington on Jan. 15, 1980, and pointed out on a map the location of the top-secret NSA intelligence-gathering system, referred to as Project A in the trial.

Project A has been described by NSA witnesses as a specific set of NSA equipment that was developed in 1975 to intercept transmissions on a particular Soviet communications link. Well-informed sources have told The Washington Post that the location that Pelton allegedly pointed to on the map was in the Sea of Okhotsk between the Kamchatka Peninsula and the eastern Soviet coastline.

The sources told The Post that after Pelton's disclosures, the Soviets were able to uncover the operation and that the U.S. government later discovered physical evidence that the operation was compromised.

Pelton, 44, worked for NSA for 14 years before leaving the agency in 1979. He is accused of selling the Soviets information about five top-secret U.S. intelligence projects in return for $35,000. His contacts with the Soviets allegedly began in 1980, shortly after he left NSA and filed for bankruptcy, and continued until his arrest last year.

Several news organizations, including CBS News and the Baltimore Sun, have filed motions requesting access to the map, which was introduced as evidence and shown to the jury Wednesday. The map carries a classification level above top secret, and the government has submitted a classified affidavit to U.S. District Court Judge Herbert F. Murray, urging that it remain secret.

Informed sources have said that U.S. intelligence officials are concerned that public release of even the approximate location of Project A might complicate relations with the Soviet Union. Prosecutors in the Pelton case have said that releasing details about Project A and the four other top-secret projects Pelton allegedly disclosed to the Soviets could provide valuable information to other nations interested in learning about U.S. intelligence-gathering capabilities.

Crowell described himself as the chief of all U.S. signals intelligence efforts directed at the Soviet Union. He said he has "several thousand" people working under him at NSA and around the world and an annual budget of "several hundred million dollars."

As part of his responsibilities, Crowell said, he regularly briefs Defense Secretary Caspar W. Weinberger, CIA Director William Casey and top military and intelligence chiefs throughout the government.

For part of the day, Crowell turned the courtroom into a lecture hall on signals intelligence, standing before the jury with charts and diagrams that outlined NSA's mission and the steps used in managing the U.S. signals intelligence program.

He played four recordings of signals typical of those that NSA intercepts. The jury heard different high-pitched tones over loudspeakers in the courtroom, and Crowell introduced the last of the recordings, one from a facsimile machine, by saying, "It's one of my favorite sounds." What emerged from the speakers was the sound of rhythmic static.

Crowell concluded his lecture by saying it was the job of signals intelligence analysts to "put yourself in position to be able to intercept, to collect signals between two terminal points." From there on, Crowell said, it is a matter of applying cryptanalysis techniques to turn raw and scrambled signals into useful intelligence reports that can be furnished to government policy makers.

Crowell's testimony about the specifics of the Pelton case was interrupted frequently by long conferences between the judge and the lawyers in the case. In an unusual development today, NSA general counsel Elizabeth Rindskopf, who had not appeared previously at the trial, joined lawyers at the bench and argued the agency's concerns about possible disclosures by Crowell when under defense cross-examination.

During much of that bench conference, which lasted nearly an hour, the official court reporter was instructed not to record the discussion. Murray has ruled that transcripts of all bench conferences in the trial be sealed, whether or not they deal with classified information.

Crowell, the government's last witness, was asked by prosecutors to assess whether Pelton would have had reason to believe that his alleged disclosures about five NSA projects could harm national security. Testifying as a government witness, Crowell said he believed that Pelton's alleged disclosures were damaging. He focused in particular on what the Soviets could have learned from an "encyclopedia" Pelton wrote on Soviet communications entitled the Signal Parameters File.

FBI agents have testified that Pelton told them the Soviets were interested in everything contained in this compendium of more than 60 Soviets signals, which included detailed information on frequency and modulation and a description of the form of encryption.

Because NSA intercepts only a small portion of the total communications of the Soviet Union, Crowell said Pelton's knowledge of which signals NSA was intercepting would have been extremely helpful to the Soviets and would allow them "to capitalize on our weaknesses."

"It will allow them to make changes in signals if they knew they were being subjected to some level of exploitation," Crowell said.

With the information from the Signal Parameters File in Soviet hands, Crowell said, "many of the capabilities we've invested to collect signals like this are extremely costly, and many of them could be rendered ineffective."

At the end of Crowell's testimony, Pelton's defense attorney, Fred Warren Bennett, filed motions for acquittal on two of the six counts in the indictment against Pelton. One count, charging that Pelton attempted to deliver classified information to the Soviet Union at its embassy in Washington, was challenged on the basis that the government had not proved that the crime was initiated in Maryland, where Pelton is on trial. Prosecutors called an FBI witness this morning in an attempt to establish that Pelton must have been in Maryland when he first telephoned the embassy because, according to tape recordings played in court, he said that it would take him at least a half-hour to get to the embassy from where he was calling.

Bennett is also seeking a judgment of acquittal on a charge that Pelton attempted to deliver classified information to the Soviet Union in April 1985. Pelton failed to make contact with Soviet officials that month when he traveled to Vienna, Austria, where the government alleges he had previously been debriefed by Soviet intelligence agents.