A FORMER police station sergeant, who had several times been commended for his work, was jailed for three years by the District Court yesterday for handling stolen cars and car parts. After a 60-day trial, Chung Chun-yam, 33, was found guilty of six counts of handling stolen goods between 1989 and 1991. He was acquitted of two similar counts. Judge Jackson said the defendant was the prime mover in a sophisticated ''ringing'' operation which involved a number of people. The court was told that engine and chassis numbers of stolen vehicles were changed to numbers belonging to wrecked cars. A second method involved using parts from a stolen car to rebuild a legitimate vehicle. The vehicles were then sold. Judge Jackson said it amazed him that Chung had devoted himself to the illegal operation in the New Territories yet at the same time held his post as a police station sergeant. Besides losing a promising career, the judge accepted that Chung, as a former police officer, would also find prison life harsh. Defence counsel Michael Poll said his client joined the force as an officer in 1977, and was promoted to his present rank in 1988. Chung was the youngest in his grouping so promoted, said Mr Poll. His submission was echoed in a report by senior force psychologist Eddie Li, who said Chung was a high-flying junior officer who was promoted to station sergeant at the age of 28. He said Chung had been under substantial stress in the two years since his arrest in April 1991. Chung had contemplated suicide more than once, said Mr Li. Judge Jackson said Chung, besides bringing disgrace to his family, had also betrayed the trust of the police force and the public. Chung's wild and unfounded complaints and allegations against colleagues during police investigations and the trial were disgraceful, said the judge. ''It is impossible to say how much he had profited in this operation, but it would be reasonable to infer that it was not insubstantial. Otherwise the defendant would not have put his career at risk,'' he said. In his defence, Chung claimed that he had bought the cars and parts from a garage called Tin Shing Motors at Kam Tin Road, and had no idea they were stolen goods. Chung offered to show police where the garage was after his arrest but they could find no such garage at the address.