China has accused the Soviet Union of a "despicable act" against a Moscow-based Chinese diplomat, saying Soviet agents had threatened to kill him unless he defected.

The accusation was made public today after the Chinese handed a scathing protest note to the Soviet charge d'affaires here earlier this week. The official New China News Agency said two Chinese diplomats arrived in the Soviet city of Minsk Aug. 17 on their way back to Moscow after a business trip to West Germany. The two were put in separate rooms "on the pretext that no double rooms were available."

At midnight, two Soviet security agents burst into the room of Wang Haiyan, and "tried to force him to agree to cooperate with them" the report said. When Wang resisted the Soviets falsely accused him of collecting intelligence and of "illicit relations," the news agency dispatch said.

"They openly threatened that if Wang refused to comply," said the agency, "they would create a traffic accident to kill Wang" and his compatriot on their way back to Moscow. The story does not say how Wang resisted the threats, or what happened on his trip to Moscow. But there have been no recent reports of any Chinese defections in the Soviet Union.