HAN Dongfang was far from pleased when I ambushed him en route to Kai Tak airport at the start of his attempt to return home to Beijing. The veteran labour activist knew any hope of success depended on absolute secrecy - and now the presence of a reporter meant his mission was in danger before it even started. After a tip-off and three-hour wait, I intercepted Mr Han as he stepped off a ferry in Central last Thursday. ''Good morning, Mr Han. Will you leave Hong Kong today?'' I said, aware he intended to try to end his four months of mainland-imposed exile in the territory. After insisting I be allowed to accompany him on the journey, Mr Han retreated into a private conversation with close friend and human rights activist Robin Munro, the Hong Kong director of Asia Watch. He reluctantly signalled his consent, and so began a hasty dash to the airport to catch Dragonair's scheduled 3 pm flight to Beijing. From the moment Mr Han set foot in the airport concourse at 2 pm, it was clear the authorities had been tipped off about his plans. A surreal atmosphere prevailed as 10 men from the Royal Hong Kong Police stood by while Mr Han joined the check-in queue for flight KA330. The police made no attempt to interfere but, with his face well-known from previous publicity, Mr Han was instantly recognised by passers-by. It was when Mr Han, 30, got to the front of the check-in queue that problems began. As soon as he handed over his passport it was passed to four Dragonair officials, milling around behind the check-in counter, who examined it in microscopic detail. ''Your passport shows you have overstayed in Hong Kong,'' one official said. This was the least of Mr Han's worries. His visa had been repeatedly extended since the Chinese Government first threw him out of his country in August, and officials at Hong Kong's Government House have made it clear he will be allowed to stay as long as he wants. ''I haven't!'' he answered the officious Dragonair staff. ''The Immigration Department sent me a letter allowing me to stay in Hong Kong until the 22nd of this month.'' He said he had not brought the letter with him. ''That's all right. I will check with the Immigration Department for you,'' the official said. As the clock on the wall reached 2.20 pm, Mr Han cleared the first hurdle. ''You can check in and go now,'' the official told him. Walking together into the restricted area for departing passengers, I asked Mr Han how he was feeling now he was a step closer to home. He remained cautious. ''I haven't got on the plane yet,'' he said. But as we passed through immigration and customs without any new problems, he became more optimistic. ''How do you feel now?'' I said. He responded with a smile as he sensed victory. In the departure lounge, he borrowed a dollar coin and spoke cheerfully on the phone, evidently telling friends he expected to be allowed to take off for Beijing. But his happiness lasted 10 minutes. As we approached the boarding gate, two of the Dragonair officials last seen at the check-in counter reappeared. Four policemen moved into position behind us, and then the airline men told Mr Han he could go no further. ''We are informed by the Chinese side that your passport has been cancelled, so we can not allow you to board the plane,'' said Dragonair official Keung King-yuen. The dissident's face turned pale. ''Which department of the Chinese Government told you that?'' he demanded. ''Xinhua,'' Mr Keung said. Mr Han did not give up without a fight: ''Xinhua is only a news agency. They are not official representatives of the Chinese Government . . . when I went to Xinhua before with my case, they refused to say they represented the Chinese Government.'' His counter-attack left the bemused Dragonair officials lost for words. At times, I was called on to translate, as they found their Putonghua inadequate to the task of trying to pacify an angry Mr Han. They admitted Xinhua was a news agency, but insisted Mr Han could not take the flight, and told him to leave the airport. Mr Han switched to a new line of attack. ''So, does any page in my passport show it has been cancelled? Can you find it for me?'' he said. His passport was intensively scrutinised once again, as the labour activist busied himself jotting down every detail of his encounter in a notebook. ''Mr Han, we cannot find any proof in your passport that it has been cancelled,'' Mr Keung said. ''But we have received a fax from Xinhua that it has been cancelled.'' They refused to show this to the labour activist. ''We haven't got the permission from Xinhua to produce it. But we wouldn't cheat you. How could I cheat you?'' said Danny Li Ka-ho, another airline official. That only prompted an already infuriated Mr Mr Han to lose his temper: ''How can I trust you?'' As the argument raged it became increasingly irrelevant - the clock had ticked on to 2:50 pm, 10 minutes before the plane's scheduled departure. ''You can leave the airport now,'' said Mr Keung. ''I won't go, I will wait until the last minute,'' Mr Han said. ''Why didn't you stop me when I bought the ticket?'' he said, once again moving to a new line of attack. ''It wasn't you who went to buy the ticket,'' one official retorted. As the clock struck three, Mr Han finally gave up - at least for that day - and switched his thoughts to more practical matters, asking if the unused ticket was refundable. Dragonair officials assured him it was, but added there would be a cancellation charge. ''Why should I need to pay any penalty? It is your company that did not allow me to board the plane,'' Mr Han said. Desperate to be rid of him, the Dragonair officials immediately agreed to waive the charges and then ushered him downstairs to immigration, still shadowed by four policemen. How was Mr Han feeling now, his hopes of going home momentarily raised and then cruelly dashed? ''This is within my expectations,'' he replied. Arriving back at the immigration office to complete the necessary formalities for entry back into Hong Kong, Mr Han caused further problems by refusing to hand over his passport. ''My passport has been cancelled, so it is useless to hand it over,'' he said. Immigration officers swiftly overcame that hurdle by agreeing to let Mr Han leave without passing through any formal procedures. Twenty minutes later, he emerged into the arrivals hall, vowing to friends that he would try again. His friends, however, expressed doubts. ''I really worry about him. I don't know what the Chinese Government will do if he gets home,'' said Mr Munro. Legislator Lau Chin-shek said Mr Han's health was still not good - he was returning from a trip to the United States for treatment for tuberculosis in August when he was first barred by China - and the excitement of a new bid to return home would not help. ''But he is totally determined. His mind is very clear. There is nothing in his passport that shows it has been cancelled. He still thinks his travel document is valid, and he will continue,'' said Mr Lau. Then, less than 24 hours later, Mr Han resumed his attempts to try to cross the border, boarding a train to Lowu at 5.24 pm on Friday, and arriving at the Shenzhen immigration control point by 6.30 pm. When mainland officials pushed the labour activist out into no-man's land between China and Hong Kong about 10 pm, he sat on the bridge between the two sides and - once the officials left - crossed back to the Chinese side again. That prompted China to close the Shenzhen checkpoint for an hour, stranding thousands of other passengers trying to cross the border, and causing disruption that continued yesterday. Those affected had divided opinions about the merits of Mr Han's attempts. ''I support his attempt. There's no reason for a national not to be able to return to his homeland,'' said Yuen Tak-wai. Others were less sympathetic. ''He is crazy,'' said one. ''He doesn't need to go back to China now - he will automatically be in China after 1997.'' After a night spent sleeping on the Lowu bridge, Mr Han resumed attempts to enter the mainland yesterday. But friend Richard Tsoi Yiu-cheong, who was with Mr Han when he was expelled from China in August - and has also been barred from the mainland as a result - predicted the dissident might have to give up. ''There is a limit to these attempts. It doesn't make sense to try 100 times,'' he said. ''If he tries again and again, it will give the public the impression that it is just a publicity stunt. ''The timing of this attempt is also bad, coming on the eve of high-level talks between Presidents Bill Clinton and Jiang Zemin. People will say Mr Han is playing little tricks at a politically sensitive time.''