The directors of the Central Intelligence Agency and the National Security Agency last night formally "cautioned" reporters covering the espionage trial of Ronald W. Pelton "against speculation and reporting details beyond the information actually released at trial."

The unusual statement from William J. Casey of the CIA and Lt. Gen. William E. Odom of NSA (some of whose secrets Pelton, a former employe, allegedly sold to the Soviets), said "such speculations and additional facts are not authorized disclosures and may cause substantial harm to the national security."

The statement, released to reporters, follows warnings from Odom and Casey that the government would consider prosecuting news organizations under a 1950 law prohibiting disclosure of classified information about communications intelligence. Pelton was a communications intelligence expert in the NSA, and the secrets he is charged with betraying involved communications intelligence.

In last night's statement, Odom and Casey also acknowledged that the government's case against Pelton "will include release of certain classified information involving communications intelligence activities of the United States." They added that "the decision to make use of this information in trial has been made by appropriate government authorities after careful consideration of the demands of trial and the potential harm that release of this selected data may cause the national security."

The fact that government officials had publicly instructed the news media how to cover the Pelton trial provoked comment last night from editors and civil libertarians.

Benjamin C. Bradlee, executive editor of The Washington Post, said that "after listening to the highest councils of government for a number of months, we have acted responsibly in balancing the national security and the national interest.

"We will continue to do so," Bradlee said, "but how the press covers this trial is a matter for the press to decide, not the government."

The Post recently published an article on the Pelton case after deciding to delete about 150 words after hearing senior government officials' concerns about the article over a period of months.

Los Angeles Times editor William F. Thomas said: "I must say it's the strangest statement I've ever come across in connection with a trial. As always, we simply are going to be bound by the best course for us to follow. This may or may not involve restricting the use of information we come across," Thomas said.

The chief legislative counsel for the American Civil Liberties Union, Jerry J. Berman, assailed the Casey-Odom statement as an improper intrusion on press coverage of the trial.

"It is a statement clearly intended to chill freedom of the press," Berman said. "What Mr. Casey is saying is that the press should not report additional details or speculate on what the government itself has chosen to disclose. In doing so, Mr. Casey compounds his assault on civil liberties. His warning, obviously intended to chill a free press, also threatens Mr. Pelton's right to a fair and open trial, fully reported. Such reporting cannot possibly be covered by the espionage laws of the United States and is clearly protected by the First Amendment."

A White House spokesman had no comment on the joint statement, but a White House official said he knew "of no specific sign-off request by Casey for this statement."

It was issued following the opening of the trial Tuesday and subsequent publication of news reports and broadcasts containing details and background that evidently displeased Casey and Odom.

Sources said yesterday that in deliberations leading up to Pelton's arrest and indictment, Casey had been among the officials who argued against putting him on trial for fear that sensitive secrets would come out in court. Official sources had said earlier that there was a battle between those who favored prosecuting Pelton and those who wanted to avoid a trial and the attendant publicity.

Disclosures made in testimony by an NSA official on the first day of the Pelton trial caused "lots of heartburn" and "raised lots of eyebrows" among senior military officers yesterday, informed sources reported. However, these sources said, those military and intelligence officials who had been involved in preparing the case knew what to expect in the way of disclosures, and were not alarmed, the sources added.

Justice Department officials acknowledged that the disclosures in the trial were unprecedented, but said they had carefully considered the legal ramifications before deciding to make some of the most sensitive evidence public. The script for the prosecution was drawn up in the Criminal Division's internal security section in consultation with intelligence officials, a Justice Department source said.