A "fun jog" planned on the fringe of the Moscow Olympics by 37 American sports fans turned a bit sour today when Soviet authorities tried to turn it into an antiboycott propaganda event.

David Himmelberger, 1978 U.S. race-walking champion, had planned a quiet early morning run with fellow Americans across the gently sloping Lenin Hills overlooking the Moskva River.

The site was changed because the Lenin Hills are a security area. Then the Soviets changed the complexion of the run.

"It's all gotten out of hand," the 34-year-old Himmelberger said when 30 Soviet and Western reporters turned up with TV cameras and tape recorders to cover the event.

The Soviet tourist agency Intourist had alerted the Soviet press to the planned run and Soviet press tipped off Western newsmen, billing the jog as a protest against President Carter's Olympic boycott.

Instead of taking a quiet run across the Lenin Hills, the Americans found themselves marshaled into three tourist buses and assigned a 3.3 mile circuit near the river.

Soviet officials sent an ambulance, three nurses, uniformed militia to hold up traffic and a swarm of plain-clothes men to lurk under trees with walkie-talkies wrapped up in newspapers to make them inconspicuous.

"We knew things were going too far when they got in touch with the Olympic organizing committee and said they could get a stadium for us," Himmelberger said.