AFTER THE MASSACRE of pro-democracy protesters in Beijing two years ago, a remarkable underground railroad safely smuggled more than 130 of China's leading dissident students and intellectuals to the West under the noses of the Chinese secret police.

Details of the effort -- unofficially called Operation Yellow Bird -- have never been disclosed for fear of compromising future missions or those involved. But the rescuers say that Chinese State Security -- the secret police -- has extensive knowledge of their operations after one escape went badly wrong. And so for the first time, in an interview with BBC television's Panorama television program, some of the organizers have revealed details of an operation that took on and largely outwitted the security services of a communist police state.

The operation involved more than 40 people. It sprang to life shortly after the Beijing crackdown, when the conservative regime of Li Peng hunted down and imprisoned political dissidents who had participated in or supported the extraordinary month of pro-democracy demonstrations in the heart of China's capital.

Yellow Bird regularly sent teams into China using the cover of specially formed trading companies. It provided false documents and disguises for the hunted men and women, and on five occasions, escape teams sent in from Hong Kong included makeup artists who helped disguise the fugitives. The escape network had access to a variety of boats and equipment normally associated with covert intelligence operations: scrambler phones, night-vision gunsights, infra-red signalers. In addition, Yellow Bird also included: Armed clashes with Chinese coastguards on the high seas. The help of Asia's mafia, the Triads. Covert support of many Chinese military and security officials.

Among those rescued were six of China's most wanted students, including Wuer Kaixi and Li Lu; two of the most senior government advisers and reformers, Chen Yizi and Yan Jiaqi; and one of the most wanted intellectuals, Su Xiaokang.

The operation had its roots among pro-democracy sympathizers in Hong Kong. In May 1989, these persons had formed the "Alliance in Support of Democratic Movements in China," and within two days of the People's Liberation Army crushing of the Beijing Spring on June 3-4, the sympathizers decided to assist those on the run inside China. They drew up an initial list of 40 dissidents they believed could form the nucleus of a Chinese democracy movement in exile. An individual associated with the group began building an escape organization.

Chinese authorities have accused John Sham, an entrepreneur and former Hong Kong actor, of being behind the operation. Sham declined to comment on the accusations beyond conceding he knows some of the details about Yellow Bird. "The operation had two immediate difficulties," he said in a BBC interview. "How to locate the dissidents who were dispersed throughout China and how to extract them."

Getting the dissidents out appeared the easier problem to solve, for a number of smuggling networks operate between China and Hong Kong, regularly smuggling anything from air conditioners to television sets to Mercedes cars into the mainland in sampans and other boats that ply the crowded inlets and islands off China's southern coast -- and smuggling out illegal immigrants seeking work in capitalist Hong Kong. Fishermen run many of these operations, but some are also organized by Asia's societies of organized crime, the Triads. The rescuers decided that only the Triads had the networks and contacts to ensure success of their effort.

"They turned to the professionals, to the smugglers," said Sham.

The Triads, ancient criminal societies with their own initiation rites and hand signals, are worldwide networks with annual income estimated in the billions of dollars. Hong Kong's three main Triads are K 14, Sun Ye On and Wo Shing Wo. They control the territory's lucrative gambling, vice and entertainment industries. Hong Kong police estimate that smuggling into China totaled $2 billion in 1990 alone.

Within a week of the Beijing massacre, one of Hong Kong's most powerful dons met with the organizer of the rescue operation at the Regal Meridien Hotel in Kowloon and readily agreed to help. "They were ideologically sympathetic to the democratic movement," said Sham. "It was certainly not because of the money." The Triads agreed to make no profits but requested that their operatives on both sides of the border be paid. An average rescue cost $5,000 although some prominent leaders cost as much as $70,000. Although the Triads made important connections, most of the smugglers involved in the rescue operations were not Triad members.

Despite widespread Hong Kong support for the democracy movement, rescue money was raised quietly for fear of arousing British authorities, who are intent on not offending Beijing before the colony is returned to China in 1997. But in a few days, Yellow Bird raised $2 million from the colony's business community. Before the rescue could begin, however, the dissidents had to be found. At least a thousand people had been killed in and around Tiananmen Square, and many dissidents fled the capital in terror. Troops and security police roamed the streets with wanted lists, and the Beijing railway station was a dangerous place. "Wherever you looked was a sea of green, uniforms of police and army," recalled Wuer Kaixi, a well-known student leader. "They checked everything -- and nobody smiled. Everybody had a very cold face."

Chen Yizi, whose liberal think tank had advised the ousted premier Zhao Ziyang, recalled the scene in one railway car. "All were panic-stricken, in disbelief. People were shattered; they argued and cursed. It was chaos."

Going underground in China is hazardous. Every residential block or hutong has its arm-banded committee under the control of the police: In previous repressions they had proved energetic informers. This time, however, although some students were turned in to police, many were protected by sympathizers.

Wuer Kaixi recalled the moment he was recognized on the train. A man looked him in the face and said, "It is a great honor to see our leaders here. And don't worry, all of the people in this wagon will help you. But face out! Face out so the guards don't see your face."

As dissidents drifted south, they encountered not only individual gestures of support but ad hoc networks of sympathizers.

Su Xiaokang was on the wanted list for his film "River Elegy," which enraged some senior Communist party officials for attacking China's backwardness. Adopted by a group of sympathizers, he was moved from place to place. "Someone would come and tell me that a contact was arriving to take me on." This individual would book a room in his own name and Su Xiaokang would stay there. "Whenever I had to leave town, I couldn't go to the station. I used a long-distance bus. I was always accompanied by one or two people. They were guiding me but we pretended not to know each other." Some of the guides were to pay a heavy price. One man who assisted Chen Yizi got 12 years in prison; another was tortured and is now mentally deranged.

Once in the south, many dissidents became vulnerable. Some heard of an escape organization but did not know how to contact it. Chen Yizi tried to slip across the border only to see his name on a list in the border post. He fled. Bai Meng, who was editor-in-chief of the broadcasting unit in Tiananmen Square, once jumped out of a window to avoid a police raid and later was seized by a gang who demanded money, claiming to know his real identity.

The Hong Kong group began receiving information about where dissidents were hiding. Great care was taken to confirm that the dissidents were genuine. Su Xiaokang recalled that the organization's first contact was to show him a photo of his son. "I had been on the run for more than two months. When I saw my son's picture, I could not control myself any longer, and I burst into tears. They had discovered I was the right person."

In the case of Wuer Kaixi, a Polaroid photo of him was shown to the group to prove the contact was genuine. They immediately dispatched a verification team to ensure it was not a Chinese Public Security Bureau trap.

Dissidents were given guides to arrange the final escape to Hong Kong. In telephone conversations, the teams used voice scramblers.

The smugglers' power boats, with four 250-hp engines and speeds of 80 knots, could outrun both the Hong Kong police and the Chinese coast guards. The cockpits were armor-plated and the teams had night-sights and infra-red signaling devices.

One of the first successful escapes was that of Wuer Kaixi. But it nearly went wrong. He waited three nights on a beach before contact was made with a smugglers' boat and then had to swim 500 meters out to the boat through water dotted with submerged concrete posts. He reached the boat badly grazed and bleeding.

As the escape numbers grew, the smugglers relied more on their contacts in the Chinese police and coast guards. Some were corrupt officials already in league with the smugglers but others sympathized with the students. This assistance, which reveals much about the present situation in China, was crucial to the underground railroad's success. In one province, a senior police officer actually traveled in the same car as a student to get him through a roadblock. A senior secret police officer who recently fled to the West told the BBC that he and others tipped students off if an arrest was impending.

One man who went into China and commanded some of the operations said the organization had contacts in "government departments, local public security bureaus, border troops, the coast guards, even radar operators."

It wasn't always possible to evade detection. Beijing brought in a thousand military intelligence troops to try to prevent the escapes. Su Xiaokang, who had hidden in a safe house, spent two hours in a harrowing offshore speedboat chase. "I felt sick and I was sweating all over. I was gripped by terror." A coast guard patrol tried to intercept the smugglers' boat, firing "machine guns and rifles in the sky as a warning," said a rescue operative. "And then they fired on the speedboat. In order to escape we returned fire." After a running gun battle, the smugglers escaped, with one of the rescuers wounded in the shoulder. Shots were fired on at least one other rescue.

Beijing sometimes took reprisals. For example, when Chen Yizi was safely smuggled from Hainan Island to Hong Kong, hidden in a secret compartment beneath a water tank on a small cargo ship, Chinese leader Li Peng ordered reprisals against the islanders, taking more than 4,000 into custody. "Li Peng was overwhelmed with anger when he heard that I had escaped," Chen Yizi said. "I felt very bad about hearing this."

When dissidents reached Hong Kong, they were quickly hustled elsewhere. British authorities had agreed to allow Yellow Bird to continue so long as rescued dissidents left silently and quickly for a third country. The organization approached the United States as a possible haven, but when America insisted on time-consuming screening first, the rescuers turned to France, which immediately agreed to accept them. Most of the operations were successful but one failed, sending Wang Juntao and Chen Zeming, two of China's most important dissidents, to jail. The two, voices of opposition even before the pro-democracy movement, were considered by the regime to be among the masterminds of the unrest. By October 1989 they too had moved south and were in hiding.

The rescuers sent businessman Luo Haixing to meet with an intermediary. Hiding places, false names and code words were discussed. But on Oct. 13, two Yellow Bird operatives were arrested as they prepared to move Chen Zeming to Dongwan City. The businessman was seized on his way back to Hong Kong. Yellow Bird had been betrayed to the intelligence services. Chen Zeming and Wang Juntao got 13 years in prison for conspiring to subvert the government; businessman Lui Haixing got five years.

But the variety of contacts and smugglers' routes is so great that escapes continue. As a Yellow Bird commander put it, with the trace of a smile, "The network was broken. We shed a skin but we can still operate."

Gavin Hewitt is a correspondent for BBC Panorama. in London.