IT BEGAN six years ago with a long distance call from a French heroin chemist to an obscure public telephone booth in the Pocono mountains of Pennsylvania. It will end very soon, police hope, with a life sentence and massive fine for a man they believe has some remarkably illegal connections in a remarkable number of countries. Thongchai Sanguandikul finally lost his battle against extradition from Hong Kong to the United States this month to face serious heroin charges and the US authorities believe the 44-year-old Thai national represents quite a catch. He is, they say, a most unusual operator. Not only do they believe Thongchai has close connections with Southeast Asian heroin baron Khun Sa, they also reckon his sphere of influence stretches as far as the cocaine cartels of South America. He stands accused of being involved in one of the largest heroin conspiracies of all time. The network linked Thailand, Pakistan, England, Holland, Israel, Belgium, Mexico, the US and, of course, Hong Kong, where statistics indicate the drug is causing growing addiction problems among the territory's youth. Thongchai, it seems, was a busy man. He also found time to dabble in shipments of anti-tank rockets, grenade launchers and M16 automatic rifles destined for the drug kingpins of Colombia. ''This investigation really targeted the most significant heroin traffickers in the world,'' said Bill Ruzzamenti, a spokesman for the US Drug Enforcement Administration (DEA) in Washington. Or, as US attorney Wayne Samuelson put it: ''The effort was herculean, the dedication unwavering, and the result extremely satisfying.'' The case against Thongchai began to fall into place in April 1987 when a French heroin chemist, who was being tracked by the French authorities, made a call to a phone booth in the Pocono mountains. US agents were tipped off that the call would be made, but only knew that it would be received in one of 50 call boxes. All 50 phones were tapped and staked out by DEA agents eager to see who arrived to take the call. After hours of waiting, a 1976 Cadillac pulled up and a man emerged. He was later identified as Ralph Santana, who had three decades of experience in the drug trade with contacts at the highest levels. Santana was arrested on June 29, 1989, and is now serving a life sentence without parole. Investigators say Santana is a case study in the history of the US drugs war, a man who, over the years, moved from marijuana to cocaine to heroin trafficking. Surveillance on Santana revealed the existence of an emissary he was using to make the connection with the drug's source in Bangkok. An international tail on the go-between led agents straight to Thongchai, who was not on either the US or Hong Kong drug list and whose importance only became apparent when the size of the deal became known. That emissary has now turned against his former bosses and is expected to give evidence against them at Thongchai's trial, scheduled for December. But he remains in fear of his life. Two of the drug baron's brothers are still at large and wanted to face charges in the same case. The conspiracy was on a massive scale, involving an annual shipment of between 1,000 and 2,000 kilograms of Southeast Asian heroin to the US through Mexico. A major seizure of 45 kgs was made on May 7, 1989, in Bangkok and is believed to be part of the shipment. A US indictment charges that Thongchai was to arrange for the heroin to be flown on a Boeing 707 from an airbase in Thailand to Mexico, where Joaquin Guzman Loera, also known as Chappo, would take delivery and arrange storage and transportation to the US. Loera, said to be the head of the Sinaloa cartel in Mexico, is alleged to have used a series of sophisticated underground tunnels which passed beneath the Mexican/US border. Despite a lengthy hunt for Loera he was not arrested until earlier this summer after he was linked to a gunfight in a crowded Mexican airport which killed a Roman Catholic cardinal and caused a public outcry about the country's drug problem. Loera was finally arrested in Guatemala and is awaiting extradition to the US. Such a big drugs operation, involving several of the world's biggest cartels, had to have a major supplier behind it, and they do not come any bigger than Khun Sa, a man regarded as the emperor of the heroin trade. His stronghold of Ho Mong, deep in the Burmese jungle, is guarded by his personal Shan United Army. Khun Sa is said to be the single biggest heroin supplier in the world and heads the DEA's most wanted list. His organisation is responsible for all phases of the drug's production, from the growing of vast poppy fields in the Golden Triangle, an area straddling the borders of Burma, Thailand and Laos, to the refining of morphine, morphine base, heroin base and heroin. Police believe Thongchai's heroin source was a man called Na Ts'ai K'uei, considered one of the most skilful drug chemists and refinery operators around. Na is serving time in Thailand but is still wanted by the US. The traditional distribution network has been through Thailand, Hong Kong and Taiwan, to the lucrative American, Australian and European markets. Latest intelligence however, suggests that much of the heroin is now travelling across western China to Guangzhou and Shenzhen, where it is stored in warehouses and released directly to the markets when needed. Heroin addicts in Hong Kong say the drug has never been cheaper on the streets because of a glut caused by too much being released from China. Police believe Thongchai's interest in Hong Kong was not so much for the territory's value as a consumer base but to launder money. A remittance house, or underground bank, in Wing Lok Street, Western, was used to launder at least US$2 million (about HK$15.46 million) of his drug dealing money. The system is simple and almost impossible to trace. The remittance house works in conjunction with a counterpart in Bangkok. Once the Bangkok house has confirmation that the money has been paid in Hong Kong, it releases the equivalent funds in Thai baht. ''It is still pretty much the financial Wild West in Hong Kong,'' said Hong Kong Narcotics Bureau detective senior inspector Phil Wallace, who worked on the case. ''There is evidence of Colombian drug money coming through the territory now. Our legislation isn't as strong as it could be. We know of at least one remittance house that was moving US$20 million a day.'' There is no extradition agreement between Thailand and the US, a fact that has hampered American attempts to apprehend drug suspects, including Thongchai and Na T'sai K'uei. Narcotics agents had to wait until November 3, 1991, for Thongchai to leave the sanctuary of Bangkok and visit Hong Kong with his wife and two children for what could have been an innocent shopping expedition. It had taken extraordinary amounts of patience and even though the moment was near, there was still a last minute panic and Thongchai nearly slipped through their fingers. Inspector Wallace said: ''We had to send for a diplomatic indictment from America showing good reason why he should be arrested. With that we could get a Hong Kong arrest warrant. We knew Thongchai was leaving on Sunday and the indictment didn't arrive until Saturday. It was very close.'' When the inspector went through the door of the Kowloon Panda hotel at 7 am the next morning, Sunday, he found the drug baron in a room with his wife and children. ''The first thing he said was: 'You have made a mistake and got the wrong person. My name is very common in Thailand'. There was no drama,'' said Inspector Wallace. Thongchai fought against extradition for two years, but finally, on September 2, he was escorted on to a plane at Kai Tak by Inspector Wallace, who will also attend his trial. As Assistant US Attorney William Behe, who is prosecuting, said: ''It would be an understatement to say the return to the US of Thongchai Sanguandikul after a two-year extradition battle in Hong Kong is anything less than a remarkable achievement.''