VANCOUVER police have arrested 19 suspected heroin traffickers and issued warrants for 11 others in response to the growing number of overdoses attributed to high-quality heroin smuggled into Canada from Hong Kong and China. At least half of the suspects are from Hong Kong and the mainland. Royal Canadian Mounted Police (RCMP) Drug Squad Staff Sergeant Jerry Meloci said the sting surfaced a number of alleged ''cell group'' wholesalers, supplied by the Big Circle Boys and other criminal organisations in Hong Kong and Guangzhou. ''Undercover operatives were able to infiltrate lower and mid-level dealers and buy more than 500 grams of heroin . . . leading to more than 50 charges against the suspects,'' Sergeant Meloci said. He said a glut of heroin on the streets had forced dealers to compete by dropping prices and boosting quality, resulting in an unprecedented number of overdoses in Vancouver this year. Police said much of the heroin sold to undercover officers in the past few weeks was identified as number-four grade. The Vancouver coroner's office estimates that more than 150 addicts overdosed on heroin last year. Following the deaths, or near deaths of more than 40 Vancouver addicts in May alone, police announced they were preparing for a war between local gangs who were struggling to take control of the Big Circle Boys' trade in heroin to Canada as 1997 approached. RCMP Drug Squad and Vancouver Police Gang Squad members said they believed the group, also known as Dai Huen Jai , still controlled almost all of the heroin smuggled into Canada from China, a route that accounted for 75 per cent of the the heroin intercepted by authorities last year. Police said mid-level traffickers in Vancouver were also targeted because of frustration with the lenient sentences usually given to street-level dealers.