ON a humid May morning in 1987, Vietnamese security officers burst into a monastery in the Dong Cong quarter of Ho Chi Minh City and dragged out a dozen monks and their followers. Under the stone floors of the ancient temple, surrounded by faded colonial villas and potholed alleyways with small tea houses, police stumbled upon the seeds of a dying revolt against Vietnam's leaders. According to reports that would later filter out of the closed military court where they were tried, the saffron-robed monks fought with pointed sticks and knives alongside ''foreign infiltrators'' trained abroad. It was the link Hanoi had long sought to establish between the fiercely independent Buddhist movement and remnants of the former South Vietnamese army seeking to overthrow the communists who defeated them in 1975. Six years later the muted rumble of dissent is threatening to boil over again in Vietnam's monasteries following unrest in the historic city of Hue, long recognised as the symbol of Buddhist power. A senior monk was hauled in for questioning after one of his followers burned himself to death in the 150-year-old Linh Mu pagoda in protest at sweeping arrests by internal security police. The self-immolation, on May 21, led to street protests by monks, including a reported clash with police after they blocked a key road. Seeking to play down the incident, Hanoi claimed last Monday that the monk had committed suicide over an unrelated domestic dispute. BUT in an interview with the official Communist Party daily Nhan Dan, Hue major Le Van Anh charged that Buddhists had burned a police car and used the protests ''to sabotage social order and security''. Western tourists who witnessed the incidents said they were taken in for questioning and had their film seized. They deny that any violence was used by the monks, who numbered only a few dozen. ''It was a classic over-reaction by the police. They seemed hyper-sensitive to anything regarding the temples: it obviously wasn't the first time something like this has happened,'' an American tourist said in Bangkok. The arrests were directed at prominent Buddhists who are pressing for an end to state interference in their faith, a legacy of the decade-and-a-half of authoritarian rule that preceded the open-door policy launched in 1988. Vietnam controls religious movements through an appointed hierarchy with communist sympathies who command little support from the grassroots membership. Dissident groups say temples are tolerated but suppressed - especially in the south, which has not had the level of party indoctrination left by four decades of disciplined rule in Hanoi. The resentment has converged with lingering anti-governmentsentiment from the aftermath of the communist victory, which led to the internment of thousands of monks in re-education camps. Labelled dissidents purely on the strength of their religious beliefs, some monks became identified with underground right-wing groups plotting the downfall of the Hanoi government from expatriate communities in North America, France and Australia. Since 1975, there have been at least a dozen recorded infiltrations involving a bizarre mixture of overseas Vietnamese, Laotian rebels, Cambodian guerillas, Thai military and - supposedly - operatives of America's Central Intelligence Agency (CIA). In March this year between 20 and 50 people, including Vietnamese from Canada and the US, were arrested with a haul of explosives and weapons in Ho Chi Minh City (formerly Saigon) as they were allegedly about to attack radio and television stations as part of a right-wing uprising. An expatriate Vietnamese linked to another overseas group was sentenced to 20 years' in jail in February for hijacking an airliner and dropping anti-government leaflets over Ho Chi Minh City. One month earlier, Doan Viet Hoat, the editor of a dissident newsletter, was imprisoned for 20 years on charges of subversion and attempting to overthrow the government. The plotters reportedly owe their allegiance to former South Vietnamese president Nguyen Van Thieu, exiled in the US since 1975, who diplomats say was in Bangkok at the time of the bombing plot. Vietnamese officials quoted some of the group arrested in March as saying they were instructed to create ''a climate of instability and chaos to undermine foreign investment in Vietnam''. Last month, Mr Thieu called for direct ''peace talks'' to arrange a transfer of power to a democratic government: there was no response from Hanoi. Overseas dissident groups say temples have become a crucial outlet for disseminating anti-government information to ordinary Vietnamese, despite evidence that the mainstream Buddhist movement distrusts both the communists and expatriates - known colloquially as Viet Krieu. MR Thieu himself came to power in 1965 after a wave of protests against the repressive regime of Ngo Dinh Diem who jailed hundreds of monks in an effort to curb the political power of Buddhist leaders. The crisis that would topple Diem began two years earlier when the president's personal guards opened fire on a crowd of monks defying a law banning the use of the Buddhist flag. Nine people were killed and dozens injured. Three days later on June 11, an elderly monk poured petrol over his body and set himself alight in a busy Saigon street in protest at the massacre. A wire service photograph of the incident snapped by an American photographer became one of the most infamous images of the Indochina war and helped galvanise public opinion in the US against the conflict. (The monk, Quang Duo, was from the same Hue monastery that witnessed the May 21 self-immolation. Reports in Vietnamese circles say the latest wave of protests partly resulted from gatherings in memory of the monk, who is revered as a leader of Buddhist dissent in southern Vietnam.) Unrest in the Buddhist and minority Catholic communities would later be exploited by both the communist Viet Cong and the opposing right wing groups. Within months of the fall of Saigon, a group called the Forces of Free Vietnam was reportedly recruiting followers in Buddhist temples throughout the south. It had connections with a Paris-based group called Vietnamese Committee for the Defence of Human Rights, whose members included the Viet Khieu hijacker jailed in February. A third group, the National Front for the Liberation of Vietnam, was allegedly backed by former American GIs and Thai military officers opposed to the communist takeover. Two months after Saigon was over-run, three former South Vietnamese soldiers allegedly established a ''Third Republic of Vietnam'' at a Catholic church in the city's Vinh Son area. When police raided the church a year later, the dissidents opened fire, killing at least one security official. In the church basement police said they found a separatist flag of three parallel red bars on a yellow background, a printing press supposed to flood the city with fake money and a cache of arms. Informers led them to La San monastery where another printing press was seized along with fake identity documents and a radio transmitter. Arrested monks were said to have ''tried to set up armed forces to occupy some regions using religion''. The security operation at Dong Cong monastery on May 1, 1987, supposedly confirmed the three-way tie between the overseas Viet Khieu local activists and religious groups. After finding a ''secret tunnel network'' filled with right-wing propaganda, Hanoi alleged in court hearings that the dissidents were affiliated with the Van Hann Institute of Buddhist Research, a legitimate religious sect. Dozens of alleged plotters have been executed by firing squad, including two leaders of the abortive 1975 plot. Diplomats say the show trials conducted through the 1980s were designed to identify religion as a subversive movement. Buddhist groups in Paris have warned that a wave of self-immolations by monks is likely in coming months to draw attention to their ''Stalinist'' persecution. ''I am now a body without a soul a dead man on furlough,'' one monk who intends to kill himself was quoted as saying.