The Kremlin today stepped up a media campaign against alleged U.S. espionage activities by describing how an American diplomat was caught "red-handed" while retrieving secret documents from the side of the road last weekend.

The new details of the alleged incident, which led to the expulsion of U.S. diplomat Lon David Augustenborg yesterday, coincided with articles designed to prove that the South Korean airliner shot down two weeks ago was also on a spying mission.

The aim of the present campaign appears to be to convince Soviet citizens that the Soviet Union is the victim of a ruthless and well-coordinated American espionage effort.

Accusing "American special services" of escalating their hostile activities, the Communist Party newspaper Pravda today said that the aim was to undermine the Soviet Union's military readiness and penetrate secret installations.

"Military, economic and political espionage is part of the general policy of the Reagan administration," Pravda said. "They spy on their own people living in the U.S., they spy on their allies and they spy on socialist countries."

The newspaper said that Augustenborg, who served as a vice-consul at the U.S. consulate-general in Leningrad, was the American control officer of a Soviet agent assigned to collect secret information about the Soviet Navy.

Describing the events that led to Augustenborg's detention, Pravda said that the U.S. diplomat, his wife Denise and their daughter went on a drive into the countryside around Leningrad, where Denise Augustenborg got out of the car and picked up secret documents.

The newspaper said that she was arrested after throwing the container with the documents into the rear seat of the car. Her husband tried to get away but was stopped, it said.

The U.S. Embassy in Moscow has declined comment on the case--its usual practice when diplomats are expelled--but the State Department has protested against what it said was the "physical mistreatment" of the Augustenborgs.

Another Soviet newspaper, meanwhile, published an account of how the pilot of the South Korean Boeing 747 had tried to evade Soviet interceptors when the plane was shot down by interceptors over Sakhalin Island Sept. 1.

The report in the Army paper Red Star said the South Korean pilot had attempted to lose his pursuers by lowering his wingflaps and losing speed. The aim was to allow the Soviet jet to dash past and slip away while it was making another approach, it said.

The pilot of the Su15 that shot down the jetliner was quoted by Red Star as saying: "I did not fall for that trick, and the pilot of the intruding plane realized this immediately. He retracted the flaps and gained maximum speed again."

The pilot's account of the last moments of the South Korean airliner square at least partly with transcripts released by the United States of his conversations with ground control. The transcript shows that the pilot reported that his "target" was decreasing speed.

A second Soviet pilot who intercepted the flight over Kamchatka said the Korean pilot "knew his onions very well."

"You know how he maneuvered after spotting me? He began wildly varying his course, altitude and speed. He saw me perfectly well," the pilot told Red Star.