Three years ago the Pentagon notified John Tillson, a civilian executive in the defense manpower and logistics office, that he was going to be fired. He had flunked three lie-detector tests administered by the Pentagon to find out who had told me about an embarrassing -- and secret -- briefing within the Defense Resources Board. That board, made up of top Pentagon civilian executives and the Joint Chiefs of Staff, had been warned on Jan. 7, 1982, that paying for President Reagan's rearmament program might well cost $750 billion more than projected over the next five years.

Frank C. Carlucci, then deputy secretary of defense, had chaired the meeting. He exploded over the story that appeared in The Post on this discrepancy. He ordered an investigation, complete with polygraphs, to find who had leaked it.

Carlucci himself, the service secretaries, the chairman of the Joint Chiefs of Staff, and Tillson, who had shown the slides at the secret meeting, were among those strapped to lie detectors. Only Tillson flunked the polygraph tests. This decorated Army combat officer received official notice that he was to be dismissed.

I have always suspected the needle jumped at the mention of my name only because we knew each other when he worked for the Senate Budget Committee staff. But whatever the reason, he was in fact absolutely innocent. I had not talked to him and did not even know he had been in the room during the presentation.

Tillson succesfully fought to keep his job, and this year his boss, Lawrence J. Korb, assistant secretary of defense for manpower, recommended him for an outstanding service award. Tillson, along with many others, did not make the White House cut of the long list. Even if he had, an award from a government that had falsely accused him could not make up for his pain, humiliation and expense.

Nonetheless, Congress, in its rush to do something -- anything -- to prevent another Walker espionage case, is on its way to risking new "Tillsons" in regard to the use of lie detectors at the Pentagon.

The House on June 28 voted 333 to 71 to require the Pentagon to conduct random polygraph tests among the roughly 4 million government and contractor personnel with access to sensitive information. The lawmakers were so lathered up over the Walker case that they batted away, on a 281 to 121 vote, a more thoughtful amendment by Chairman Jack Brooks (D- Texas) of the Government Operations Committee. Having taken a long look at lie detectors, Brooks pleaded in vain with his colleagues not to give in to hysteria -- to at least wait for the results of a study in which the Pentagon is giving 3,500 people polygraph exams and assessing the results.

"There is no scientific basis for relying on the polygraph as a valid indicator of veracity," Brooks warned. He said Soviet agents are trained to beat polygraph tests. John F. Beary III, a medical doctor who served as assistant secretary of defense for public affairs, has warned on the basis of his own study of the evidence that "no machine can detect a lie. The machine can only detect stress; however, the stress may result from several emotional causes other than guilt, such as fear, surprise or anger. . . . The polygraph misclassifies innocent people as liars."

House backers of the broad lie-detector amendment contend people who would be wired would be questioned only about contacts with foreign agents and unauthorized release of classified information. But this is no limitation at all in the real world of the Pentagon. There, virtually every piece of enlightening information bears some kind of classification cover. The briefing paper about the $750 billion gap between rhetoric and reality was classified, for example, although Sen. Sam Nunn (D-Ga.) and the Pentagon saw no damage to the national security in holding an open Senate hearing on the issue after the story broke. Beary's memo on the flaws of the polygraph also was classified when first presented.

Members of the Senate and House armed services committees are now hammering out a compromise version of their rival 1986 defense authorization bills, with the House polygraph amendment one of the questions at issue. The recent arrest of Sharon Marie Scranage, a CIA employee, on charges of giving secrets to a Ghanaian, is expected to strengthen the hand of the House conferees. Suspicions about her were aroused by her reactions during a routine polygraph test. And whether lie detectors are reliable or not, it can be argued that the threat of being wired to them scares and inhibits people.

Widening their use would indeed make it more difficult for reporters, senators, representatives, government staff people, pressure groups and plain citizens to find out what is going on inside the Pentagon. But I doubt the Russians would lose much from this intimidation of the bureaucracy. The record shows that the Soviets in most cases obtained the really sensitive information through old-fashioned espionage: buying secrets from dishonorable people who could probably beat a lie-detector test.

Before they submit millions of Defense Department employees to the threat of the polygraph which indicated an innocent Tillson was guilty, the lawmakers should ask how knowledgeable they and other Americans can expect to become on questions of national defense if a blanket of intimidation is allowed to fall over the Pentagon. The writer is on the national staff of The Post.