JOHN Chan Cho-chak, who turns 50 on April 8, must have had a laugh or two during the past months. Whenever a civil service re-shuffle was announced, the diminutive Education and Manpower Secretary always appeared in the post-announcement analysis, whetherhe was affected by the events or not. This obsessive media interest in Mr Chan's career has been mostly based on the assumption that his future was pivotal to a much grander plan. Executive Councillor Mr Chan, the commentators said, was destined for one of the big jobs. Perhaps as Chief Secretary when Sir David Ford retires, but more likely as the chief executive most acceptable to all parties when Hongkong returns to Chinese sovereignty in 1997. That was the key to his present low profile, the argument went. He would lie low, not saying a public word about the Patten democracy proposals, while Beijing and London failed to reach a compromise. When all the hard work was done, Mr Chan would emerge from the civil service shadows, untainted by unpleasant associations of supporting enhanced democracy and take capable hold of Hongkong during the transition. As it turns out, none of the above assumptions is true. They appeared plausible, but they were wrong. Yesterday we learnt the truth. Mr Chan resigned several months ago, long before two major government re-shuffles, but the small group of people privy tothe information kept their counsel. He informed Governor Patten and, presumably, some members of Exco, and he retreated into his discreet shell. He has told few people outside his family why he has chosen to go, but he will remain in his present job until June and continue to sit on Exco until he departs from office. Without exception, those who were informed respected his wish to keep the reasons for the decision in the family. The general view is that no one else knows why Mr Chan has chosen to go at the peak of a brilliant and harmonious career. Most of his colleagues were astonished by the announcement two days ago. Tributes came spontaneously from the civil service trade unions and current and ex-staff members said they could not think of a bad word to say about him. It was generally agreed that Governor Patten had an excellent relationship with the Exco member. In this context, his decision to retire becomes all the more problematical. If he is regarded as an impeccable, highly competent policy maker who has not publicly opposed the Patten proposals, why did he go, especially when he is paid $130,000 a month (including the 1992 pay increase) plus the usual civil service perks package. IN interviews after his announcement he ruled out one obvious answer - failing health. He had just had a full medical, he said, and there were no problems. He also tacitly agreed that he was happy in his work. Is he then about to take a job in the private sector? That option could present some immediate problems to his employer. As a member of Exco, elevated to the post last October, Mr Chan is an influential member of the territory's ultimate decision-making body. He has taken part in some of the most controversial policy decisions undertaken by the Hongkong Government in the past decade. Added to that, is his control of the Education and Manpower portfolio - always a difficult job, but lately more so with the problems of rising child suicides, falling standards of English and the implementation of an electorally unpopular labour import scheme. Access to such confidential information means he cannot walk into a high-level job a month or so after his retirement. It is accepted that an Exco member has to endure a period of at least 12 months' ''sanitation'' - unemployment - before he can accept a non-government job, especially at Mr Chan's expected level of entry. This option is all the more puzzling because the policy secretary, who lists ten-pin bowling and performing in Cantonese opera as two of his main hobbies, has always been regarded as the ultimate civil servant - totally discreet, meticulous in his work, assiduous in his attention to detail, very articulate and perspicacious in his judgement. A former staffer recalled yesterday her experience with him when he was the Director of Information in 1986. He attended the weekly Exco meetings, as an observer, she said. When he came back to the office he would have to tell her how certain matters had progressed during the morning. ''I would have the agenda, which was numbered in the normal way. He would say: 'Item one: yes; Item 2: OK; Item 3: No.' He was so discreet about the subject of the meetings that he would not risk saying them out loud. He adheres strictly to the code of the ultimate, objective civil servant.'' That discretion has its advantages when it comes to another of Chan's interests - the racetrack. Whenever he goes to the races, often with fellow members of the Hongkong Club, he is amusingly secretive about his bets. ''He keeps all his tips to himself and never says how much he has put on a horse. Even when he wins you would not know,'' the former colleague said. FRIENDS of Mr Chan who volunteered their opinions about his decision held similar views. They would not countenance the suggestion that he had retired early, to prepare for a comeback in later years. ''He is not the type of man to play that sort of game. He is the ultimate civil servant. If he does have a job to go to, you wonder whom he would work for, and what he would want to do instead of his present job,'' another said. Perhaps it is simple. Four years ago, in an interview with the South China Morning Post, Mr Chan, then the Trade and Industry Secretary said: ''I don't take directions from London in the job I do now and the Hongkong administration will not be taking directions from Beijing in 1997. ''It is important to remember that the day-to-day government of Hongkong in the half-century after 1997 will be in the hands of people like myself and my colleagues in the administration. '' His career had started slowly then developed at high speed. Born in Hongkong during the Japanese occupation in 1943 and sent to China soon after. His grandfather was a famous Chinese herbal medicine doctor, whose son came to Hongkong to try his luck. Mr Chan senior began his working life as a clerk in the Dodwell group and rose to be chief accountant. Chan Cho-chak had a Catholic education with the Jesuits at Wah Yan College, Kowloon. He completed his A-levels at the famous La Salle College and was accepted at Hongkong University as an undergraduate in 1966. He graduated with a BA honours degree, andfound his way into government as an executive officer in the trade department. Six years later, he moved across to the fast-track administrative officers grade, where he specialised in trade but developed a reputation as an all-rounder. He left government for the private sector, joining Sun Hung Kai in 1978, but returned in 1980, when, identified as a high-flier, he assumed a number of senior positions. He oversaw the controversial debate on the Green Paper for legislative reform, and despite having to defend the Government's backdown on its promise for greater democracy, he managed to retain the respect of the liberals during an antagonistic debate. During the past three years, first as Secretary for Trade and Industry and then as Education and Manpower head, he faced awkward issues - trade embargoes, the controversial Hospital Authority transition and attacks on the Government's education and welfare funding. With this record, and his unblemished profile as an administrator and model family man - he and his wife Agnes, and children Peter and Catherine, have lived comfortably on western Hongkong Island for the past few years - something very important must have happened to make John Chan change his life at such an interesting and portentous moment in history. Knowing him, somebody else will probably tell us before Mr Chan does.