WHEN a series of satellites began rocketing off launch pads at California's Vandenberg Air Force Base in 1960, the US government told the public that their purpose was to analyze the hostile climes of outer space.
In fact, the space probes were eyeing hostility much closer to home: missiles in the Soviet Union, nuclear weapons tests in China, and military movements worldwide.
Now, 35 years later, the Central Intelligence Agency (CIA) is revealing the truth about one of its most closely guarded and revolutionary projects -- code named Corona.
The revelations, which came at an unprecedented two-day CIA seminar at the George Washington University here beginning May 23, have piqued the interest of academics, historians, and environmentalists, among others.
One of the program's highpoints was when the Corona satellites dispelled the notion of a ''missile gap'' -- the idea in the late 1950s and early 1960s that Moscow had a huge lead over the US in nuclear missiles. Corona photos of Soviet sites led the CIA to conclude that the Soviet force ''represents only a limited threat....''
Corona photos also pinpointed when China would detonate its first atomic bomb. An August 1964 CIA report says that a suspected test site in western China ''could be ready in about two months.'' The first blast occurred October 16. A Corona photo confirmed four days later that China had become a nuclear state.
The official line that the ''Discoverers'' -- as the satellites were publically known -- were for space research, was part of an elaborate cover story. In fact, the only satellite designed for space research crashed into the Pacific, killing the four black mice on board and provoking an outcry by animal rights groups. The other 16 Discoverers carried cameras, the first in a family of 145 spacecraft that photographed US cold war rivals.
The information comes in a move ordered by President Clinton last February. The CIA will turn over to the National Archives some 850,000 pictures shot between 1960 and 1972. They cover 750 million square nautical miles.
''The Corona system ... revolutionized intelligence collection analysis, and it put the cold war into an entirely different, profoundly new framework,'' says Brian Latell, director of the CIA's Center for the Study of Intelligence.
Prompted by a need to peer behind the Iron Curtain, President Dwight Eisenhower authorized the CIA and Air Force to start the Corona project in 1958. The first eight Coronas failed. The ninth achieved what for the time was a major breakthrough: an airplane snagged the parachute of the satellite's ejected film capsule as it floated earthward.
The first inflight recovery of a space vehicle on Aug. 18, 1960, could not have come at a more crucial time: three months earlier, Francis Gary Powers' U-2 spy plane had been downed over the Soviet Union, forcing Mr. Eisenhower to end the only overhead US surveillance of the country at that time. The film recovered from the first Corona mission covered more than 1.6 million square miles, more than all of the U-2 flights combined. The resolution of the film enabled the viewing of objects as small as about 20 feet across. By 1972, the resolution revealed objects as small as six feet wide.
Until they became obsolete in 1972, the Coronas helped the US plot arms control strategies, choose targets for its nuclear missiles, and prepare maps. They were also used to confirm the destruction by Israel of the Egyptian and Syrian air forces in the 1967 Arab-Iraeli war and to assess the results of US air attacks on North Vietnamese defenses.
The Coronas made other contributions. They laid the groundwork for today's sophisticated space cameras and the steering mechanisms needed for spacecraft docking maneuvers, says Katherine Schneider, an official with the National Reconnaisance Office, which now operates all US spy satellites.
''You can almost say that when the docking between the US [Space shuttle] and the Russian Mir takes place [next year], that it was only possible because of this technology that was tested and developed back in the early part of the Corona project,'' adds Robert McDonald of the National War College here.
Not only are academics and historians eager to see the material, but environmentalists and land-management experts are, too. They may see in the photographs the erosion and climatic changes in parts of the earth that occured before the 1972 launch of the first US commercial space imagery satellite.
The declassification is part of a post-cold war CIA attempt at ''openness,'' which is aimed at improving popular perceptions of an agency whose scandals are well known but whose successes have been kept secret. There are, however, limits to what can be made public: Thus some of the Cornoa material is being kept secret.