HONGKONG'S Amateur Sports Federation and Olympic Committee and the territory's most powerful man in sport, Mr A. de O. Sales, last night threw their weight behind Beijing's bid to hold the Olympic Games in year 2000. ''Time is due to give Hongkong's position on the 2000 Olympic bid, and because of our political status we must inevitably side with China,'' said Mr Sales, who as well as being president of the local sports authorities is also chairman of the influentialCommonwealth Games Federation. Hongkong has no voting rights in the International Olympic Committee board which will choose the host of the 2000 Games but support from Mr Sales could swing decisive votes Beijing's way. Thirteen members of the IOC are due to pass through Hongkong next month on their way to the mainland, having just finished examining the bid being mounted by Sydney. Mr Sales said last night he would try to persuade the group to back Beijing's bid when the final votes are cast in Monte Carlo on September 23. ''Even in 1973, in the days of the Cold War, I telegramed Beijing from Christchurch, New Zealand, urging them to join the IOC with the full backing of the Commonwealth countries,'' said Mr Sales. Mr Sales' remark was seen as implying that many Commonwealth nations would again endorse his decision to support Beijing. But with Sydney touted as Beijing's main rival, Mr Sales is in the awkward position of now backing the mainland over a fellow-Commonwealth member nation. Also competing for the 2000 Olympics are Berlin, Brasilia, Istanbul, Milan and Manchester. Mr Sales had delayed declaring his position on the preferred host. Earlier this month he refused to give an opinion despite the fact that the Sports Development Board, the Government's sports funding arm, openly supported Beijing's bid. The board's officials are hoping that the then Hongkong Special Administrative Region would be nominated by Beijing to host one or two sports. Soccer is one of the sports mentioned, especially with the Hongkong Stadium currently under redevelopment which will transform it into a 40,000-seater arena. Equestrian events could also be staged because the facilities at Beas River in Sheung Shui are up-to-date and pose no problem in accommodating horses from around the world. Mr Sales cited Beijing's success in hosting the 1990 Asian Games as the main reason for supporting China. ''The Chinese had proved they have the resources and the know-how to run a multi-sports extravaganza and it should give them an edge over the other cities in their Olympic bid.'' He said that having the 2000 Olympics in Beijing would be good for sports in China, Asia and for the Olympic movement because ''the Games must rotate - from north to south, east to west''. He said: ''In the past 100 years Asia has only hosted the Games twice and it is about time it comes back to this continent.''