It's time for the Navy to come clean.

It's time for the Naval Investigative Service to come clean on the circumstances surrounding three false "confessions" it secured last year in the affair of the Marine guards at our Moscow embassy.

The "confessions" gave credence to the notion that Marines had given KGB agents entry into every secret place in the U.S. Embassy in Moscow. Former corporal Arnold Bracy, Cpl. Robert J. Williams and Sgt. Vincent Downes all signed statements after intensive interrogation.

Bracy was supposed to have supplied the damning evidence that he and Sgt. Clayton Lonetree had collaborated to betray the United States. Williams, questioned in Austria, and Downes, in Virginia, were said to have agreed that Bracy told each he was "involved in espionage."

Now, in a carefully and fully developed investigative article in The Post {front page, Jan. 17}, Don Oberdorfer has given an account of the "Marine scandal." After months of public silence on the part of the government and lack of inquiry or coverage from the press, a great deal of shocking information has been revealed.

The NIS has concluded that there was no collaboration between Bracy and Lonetree; that "information" it claimed to have obtained under interrogation was not true. Reagan administration officials have finally admitted that the Marines didn't let any Soviet spies into the embassy. The current U.S. ambassador to the Soviet Union, Jack Matlock, has called the affair a "nonoccurring event." As Oberdorfer wrote, "the government had been grappling mostly with phantoms of its own invention."

In the process of invention, a series of suspicious events did occur, however. The government of the United States sounded the Klaxon: the national security was utterly compromised. But wasn't a lie carefully contrived to account for the peril? Its entire weight was borne by the infamous "confessions." If so, who made the decision to fake them? Who spun out the yarn? Who exercised the authority to go forward with it? Who wrote the script for the Bracy confession with its "rich detail"? These are important questions that require answers, but they are not the most urgent.

Three young black men were interrogated. All say that their statements were compelled by force . . . coercion. What happened to them?

What happened to Arnold Bracy in 29 Palms, Calif., on March 18, 19 and 20? Those are the days when he was in the hands of the NIS. He was taken from his job during an inspection, and over the objections of his commanding officer. On the 18th he was questioned by Michael Embry, the base NIS agent.

On the 19th and 20th, he was interrogated in "nearby motels" by Embry, David Hurt and Jim Pender, interrogators from NIS regional offices. They introduced themselves as polygraph operators. Why did the NIS take Bracy from the desert-flat, open, secure base to conduct official business? Its justification was the need for protection from surveillance or a "rescue" attempt. Bracy had already allowed his quarters to be searched. And they had been "tossed" on the 18th; his spy novels were taken. On the 19th he waived his remaining rights, was told that the lie detector was infallible, agreed to be polygraphed and submitted willingly to interrogation, according to one of his defenders. Over the three days of interrogation, the 21-year-old noncom signed three different progressively incriminating statements.

None holds up today.

While some details about what went on in that room remain murky, counterintelligence agents the world over, operating out of public view, use psychological intimidation to "break" suspects. Isolation from familiar surroundings, misleading statements, intense questioning, accusations, purported previous knowledge and verbal harassment are standard procedures.

Some consequences of "intense and hostile questioning" are known. A "six-page, single-spaced, typewritten statement" full of irregularities was the final document obtained by the NIS team. In the statement, Bracy "confesses" acts of treason that carry the death penalty.

Bracy's signature is on it. It is also known that immediately after signing it, Bracy protested that it was untrue. He maintains that he "was threatened into signing the statement without being permitted to read it." Williams and Downes say their statements were forced and false and, as Bracy maintains, that their contents were offered by NIS as speculation and typed out as "facts." The mass of details in the Bracy document was carefully checked later. Locks, safeguards and security systems were examined. As far as can be determined, none of these had been tampered with or compromised. Robert Lamb, who heads the State Department's Diplomatic Security Bureau, told me: "There were things in the statement attributed to Bracy that could not have happened."

The NIS claims that it has just lately conducted its own review of what went on and, according to Oberdorfer, "insists that an investigation has shown it {the Bracy confession} to have been obtained in good faith and with proper procedural safeguards." No mention is made of the Williams and Downes statements. The NIS has failed to produce anything to verify its conclusions. There is no transcript of the interrogations, no tape recording, no statement from a nonparticipating observer. It has admitted to no "misconduct" or "improper behavior" by its agents.

The Navy has no explanation for its discredited "confessions." On the contrary, its line is hard and aggressive. I was told by a Navy source: the investigation of Bracy continues; the interrogators didn't do "an A-plus job; that's not unusual; it happens to everybody." Bracy, the division lay leader at his base, who is a Pentecostal, is referred to with scorn, by this same source, and through innuendo, a clear determination to get him is expressed. When asked directly if, in light of the undocumented interrogations, the Navy considers Bracy to be guilty of espionage, the answer is, "We don't know. The investigation is continuing." (NIS agents, incidentally, do not themselves give statements unless they are tape-recorded.)

Oberdorfer reported that 1,743 people, in 35 countries, were questioned, and the Navy is not through yet. As one man on the defendants' side told me, "They're after anybody they can get. They've got to nail somebody or they're washed up."

NIS and Navy officials are involved in meetings at the Department of Justice. Though they've had to admit that the KGB didn't invade the embassy, they are clinging to their conviction that there are people out there to blame for something. A number of the Marines they thought they'd implicated are about to leave the corps. It is reasonable to speculate that the Navy is trying to get someone at Justice to help it off the hook by announcing that Justice is taking over "ongoing" investigations.

Presumably, Justice, which was locked out of the initial emergency, will not willingly step into the matter. It has no plans to look into the tainted "confessions."

No matter what Justice does about the continuing investigations, the Navy and the NIS will not be off the hook on the "confessions" and statements. They smell of more than the word the Navy hates -- "blundering." They reek of coercion and untruth.

The writer was assistant secretary of state for human rights in the Carter administration.