The Soviet Union first learned that a KH 11 spy satellite was photographing its territory when a former Central Intelligence Agency employe sold them a stolen copy of a top-secret manual describing the satellite, U.S. officials said yesterday.

The disclosures in the manual, the officials said are, apparently prompting Soviet officials to hide some weapons previously photographed by the satelite.

The KH11 "was misclassified" by the Soviets as nonphotographic satellite, sources said, so they did not bother to try to hide sensitive weapons or operations from it when it passed overhead.

Therefore, distressed intelligence officials said, the KH11 was able to look down on Russia from space for more than a year without the impediment of cover-up efforts.

The Soviets discovered their monumental intelligence error last winter when William P. Kampiles, a former CIA watch officer, sold them for $3,000 the manual describing what the KH11 could do, sources said.

Yesterday's disclosures by authoritative government sources help explain why Justice Department was so quick to prosecue the 23-year-old Kampiles, who was convicted of espionage last week and could be sentenced to life imprisonment.

The information also explains why intelligence professionals and Carter administration officials are putting different interpretations on how big a setback the loss of the KH11 manual represented.

To the intelligence professionals, the loss is a "disaster" because a prime source of vital information has been compromised.

To administration officials, the loss is a major security breach but not one that destroys the ability of the monitor arms control agreements.

The Soviets have known for years that the United States has been sending a member of different spy satellites over their territory, with those known as Samos and Big Bird among the ones it identified as picture-taking ones.

But for some reasons, the KH11 was not picked out from the clutter of U.S. satellites as a new eye in the sky - one not only equipped with advanced cameras but also able as well to transmit directly from space the pictures it took to U.S. ground stations.

Getting pictures from the old Samos spy satellites required parachuting the packets of film from the spacecraft and then having them snatched in midair by Air Force planes patrolling the drop zone.

U.S. and Soviet space trackers know the paths that each other's satellites fly and estimate the area their cameras can cover. It is standard procedure for both the U.S. and Soviet governments to conceal especially sensitive operations from these eyes in the sky as they pass overhead.

For example, a book on the CIA's Glomar Explorer mission to pick a Soviet submarine off the ocean bottom reports that the operation was concealed from Russian satellites.

"As soon as they knew that Soviet satellites had pasted the point in their orbits beyond which the Explorer was out of photographic range of their cameras," states one passage in the book, "A Matter Risk," one crewman operated the Explorer's main crane to lower a steel cable through the top of Moon Pool on the ship.

Since the Soviets obtained the manual on the KH11 photographic satellite, sources said, they have been moving some weaponry out of the range of its cameras when it passes over certain points.

Many intelligence specialists believe these concealment efforts are a direct result of discovering through the manual what the KH11 could do, although U.S. officials stressed they cannot be sure that this is the only reason.

Weapons of interest to U.S. intelligence that the Soviets can move around easily to elude satellite cameras include the SS20 mobile intermediate range missile and the controversial Backfire bomber.

However, such big weaponry as Soviet intercontinental missiles and submarines berthed or being constructed cannot be moved around to escape the camera eyes in space. Therefore, some officials argue, the United States will be able to verify the weapons that are coverted by the strategic arms limitation treaties.

This is expected to be a point of contention if a new SALT agreement is sent to the Senate with some critics contending the ability of the United States to verify Soviet weaponry has been degraded.