CHAIN gangs of shackled prisoners, including political detainees, stand up to their knees in the Len River under armed guard in Burma's eastern Shan state, breaking stones to build a road connecting China and the Thai border along which heroin, young girlsand Japanese cars are already being transported. A shuffling band of pathetic human wrecks, some clearly sick with fever, stagger from the river when they see a visitor. One says: ''Please give a few cents to help buy some necessities - and something to smoke.'' Although some prisoners may be hardened criminals, a number of them possibly addicted to heroin, others are young men barely out of their teens. The chains connect their ankles to their waists. As the prisoner begins to speak again a guard with a rifle slung over his shoulder approaches; the prisoner moves away with a handful of currency and the cheroots that Burmese, male or female, like to smoke, muttering: ''I can't say more - it is forbidden.'' As the men work, stooping into the water for stones to construct a road in place of the present track, impassable in the wet season, there is an unnerving clanking of chains. In a nearby village, a man in his 30s confides: ''My friend, a student from Rangoon, worked in chains on the road and now he is dead.'' Looking round nervously, as most Burmese do when talking to a foreigner - fear of the ruling military junta, the State Law and Order Restoration Council (SLORC), grips the whole country - he adds: ''I can't say how he died - I am too afraid to repeat it.'' Many diseases, including malaria, have been rife in these areas for years, but the man seems to hint at something else. Most students working in the chain gangs were seized in Rangoon when pro-democracy demonstrations were violently suppressed in 1988. The SLORC later arrested democracy leader and Nobel peace laureate Ms Daw Aung Sang Suu Kyi, who is still under house arrest three and a half years later, despite appeals by the Dalai Lama and the UN Security Council, among others. The 167 km journey from Tachileik, on the Burmese side of the Thai border - along a tortuous track that hugs ravines and winds through forested mountains beyond which lie the poppy fields of the world's richest opium-growing region - to Kengtung, unofficial ''capital'' of the Golden Triangle, enables the visitor to witness the Burmese gulag at first hand. ''The Burmese junta is so out of touch it does not seem to realise it is doing anything wrong, and in theory is allowing visitors, even tourists, to see this,'' a Bangkok-based specialist on Burma says. The road was closed in 1950, when Chinese Kuomintang troops, driven from China by Mao Zedong's communist armies, seized Kengtung. Later, fighting between Burmese forces and those of the Beijing-backed Burmese Communist Party (BCP), and the 7,000-strong Shan army of opium warlord Khun Sa, kept Kengtung sealed off from Thailand. After a cease-fire signed in 1989 with the BCP, which was severely weakened by an internal mutiny, and the establishment of a live-and-let-live arrangement with Khun Sa, the road was opened to foreigners late last year. THIS was partly prompted by the junta's need to end its international isolation and encourage a tourist trade in the Burmese sector of the Golden Triangle, where the borders of Burma, Laos and Thailand meet. Now there is a heavy Burmese army presence, with camps at the edge of towns and villages. Yet there is a sense that the security situation, now apparently firmly under control, could deteriorate again in future. The uneasy peace has resulted in an explosion of opium-growing by Wa and Kokang hill tribesmen, and resultant heroin production. The US State Department estimates poppy-growing areas in the Burmese section of the Triangle have almost doubled since 1987, from about 93,000 hectares to 161,000 hectares. Opium is made into heroin in refineries on the Burmese side of the Thai border, and some sources claim the ruling military junta is involved, although confirmation of this is difficult. Clearly visible at the edge of the forest near one village were ponies and mule trains transporting heavy sacks on wooden frames similar to those known to be used to transport raw opium. After refining, the heroin is shipped by couriers to Bangkok, Hongkong, Kunming in China, and, increasingly, into India and Bangladesh for onward transit to the United States and Europe. This road was last described by Dr Gordon S. Seagrave, an American Baptist missionary surgeon based in the area during World War II, as ''the most beautiful in Burma''. ''It was literally nothing but a shelf, sometimes cut out of solid rock, sometimes built up with stones from the river's bed,'' Dr Seagrave wrote in Burma Surgeon, published in 1944. ''You had to scrape the cliff to stay on the road at times,'' he added. Dr Seagrave saw Akha hill tribe women ''each with a pipe in her mouth and a bare, protuberant abdomen''. This, including road-building with stones form the Len, is exactly what travellers are now seeing as they move in four-wheel drive vehicles through bamboo and thatch Akha villages with their distinctive, windowless houses. But the visitors also see new Japanese cars without number plates bumping along from Thailand to China's Yunnan province, where the growing prosperity is fuelled by both the Chinese Government's economic reforms, and the cross-border drug trade. Last year, the Chinese People's Liberation Army launched a major military operation in Yunnan, near the Burmese border, and reports suggest it was against drug traffickers - possibly even opium-growers - who had operated with impunity in the area. The market in Tachileik is crammed with Chinese consumer goods also transported along the route now being rebuilt by forced labour. Sources in Kengtung, and in Mae Sai, on the Thai side of the border, say Shan girls, who have a milky-white complexion and rosy cheeks, also travel this road to Thailand, together with young girls procured in southwest China. The girls, many in their early teens, are on their way to work in the flesh trade in Bangkok, or even further afield. The Shan girls, who are much sought after in brothels patronised by Thais, are able to return, some already HIV positive, but the Chinese girls are sold to agents in Thailand. ''Their final fate can only be imagined,'' says a resident in Mae Sai familiar with this traffic in sexual slaves.