Nine months after a Soviet fighter plane shot down Korean Air Lines Flight 007, killing all 269 men, women and children aboard, reporter Seymour Hersh found himself summoned to Moscow. His investigative instincts stirred by the incident, whose savagery had shocked the world, Hersh, 49, was intrigued by the Soviet invitation. "I thought, 'Wow, whammo! They really have something,' " Hersh recalls. "I just assumed the Russians knew something they didn't want to go public with and maybe they would let me onto it." When he met with Marshal Nikolai V. Ogarkov, head of the General Staff, and Deputy Foreign Minister Georgi M. Kornienko at the Soviet Defense Ministry, however, Kornienko explained why Hersh had been invited to Moscow: The Soviets wanted America's foremost investigative journalist to expose what they believed was the Central Intelligence Agency's role in the shoot-down. Taken aback, Hersh asked with a laugh if Kornienko was trying to be his editor. Kornienko replied in English, "Your assignment is to find that [the airliner] was an intruder."

The Soviet diplomat was probably emboldened by Hersh's reputation for publishing stories that have embarrassed several U.S. administrations. But Kornienko apparently didn't know what any American functionary could have told him: Hersh doesn't take directions from bureaucrats. When the results of his two-and-a-half year investigation of the airliner's destruction hit bookstores last month, his findings pleased neither Moscow nor Washington. He found that KAL 007's last flight was not on a CIA espionage mission, as the Soviets claim, but neither was its destruction a totally wanton act of murder, as President Reagan alleged. Hersh's riveting book, titled "The Target Is Destroyed" alter the Soviet pilot's infamous radio message that he had fired his rockets, is a thorough analysis of the incident.

Hersh went after the story with typical relentlessness. From his rented Washington, D.C. office, he placed hundreds of phone calls and juggled the replies as they came in over two lines. "The big break," he says, "as it always is in these things, was total serendipity." Late in 1984 he received a penciled note from a U.S. military officer listing possible sources in Air Force Intelligence. That led Hersh into the clandestine realm of the National Security Agency, which runs the ultrasecret electronic listening posts that eavesdropped on the Soviets as they tracked KAL 007 on the night of Sept. 1, 1983.

Eventually some of these sources opened up to Hersh, largely out of frustration with what they viewed as the abuse of communications intelligence. "I generally feel that American intelligence officers should not talk to the press," says Air Force Major Gen. James C. Pfautz, 56, now retired, who reluctantly agreed to talk after Hersh had gleaned most of the story from other sources. "But I was dismayed at the handling of the intelligence." CIA director William Casey called Hersh as the book was being readied for publication, threatening prosecution should it disclose any classified information. "It got me very angry," says Hersh, who in fact had deleted some sensitive material on his own initiative. "I guarantee you that we in the press have as good a sense of what's important and what's good for America as the people in the CIA."

The story that emerged was not what Hersh had expected. Having originally theorized that the Korean pilot might have been trying to spy on his own inititative, he concluded that KAL 007 was simply lost over the U.S.S.R. and that U.S. intelligence did not figure out what had happened until it was too late. Within 15 hours after KAL 007 plunged into the Sea of Japan, he says, an Air Force Intelligence team realized that the Soviets had simply failed to make a positive identification of the aircraft and had attacked what they believed to be a U.S. intelligence overflight. Hersh charges that the Reagan White House first dismissed and then suppressed that information, misusing intelligence to score political points against the Russians, who worsened the crisis by choosing to appear indifferent to human life rather than admit their terrible blunder. "I find it awful that the U.S. government did not set the record straight and went around Russian-bashing," says Hersh. "This is not a story about 007. This is a story about crisis management, and we get a very bad mark and so do the Russians." In a world bristling with nuclear weapons, that's bad news, he says. "The whole notion of deterrence is that the men in charge know what they're talking about and are rational. This shows that's not the case."

Hersh hardened into a tough, go-getting reporter by starting at the bottom. Born on the South Side of Chicago, he attended the University of Chicago, then tried law school only to leave after the first year. He got his start in journalism as a gofer for the City News Bureau in 1959 and went on to become Pentagon correspondent for the Associated Press. In June 1967 he quit to free-lance and, except for a seven-year stint with the New York Times in the '70s, he has worked on his own ever since.

Hersh and his wife, Elizabeth, a psychiatrist, live in Washington's Cleveland Park neighborhood. Married since 1964, they have three children. "Sy is soft and caring with his wife and children," says Hersh's neighbor and fellow journalist Milton Viorst. "This is not a man who, because he is a tough reporter, lacks a soft side."

Hersh has attained a kind of mythic status as a journalist, which he downplays. "There's a certain amount of 'Geez, what a great reporter,' " he says. "And the story is just there, you know? Go do it, man. There's nothing you can't do in this country." With his new sources in intelligence, he says, "I'm working on something now that's terrific." In other words, Sy Hersh is ready to do it again.