IT may be that the doyen of Hongkong sport, A. de O. Sales, has thrown his considerable clout behind Beijing's bid to host the Olympics in the Year 2000. But it would seem Beijing's closest rival, Sydney, holds the trump card to scupper China's chances. The decision as to which bid succeeds rests entirely with the all-powerful International Olympic Committee. And over the next few months this bunch of peripatetic sporting apparatchiks - for whom the term ''Frequent Traveller'' might have been invented -will be gleefully anticipating regular trips to China - via Hongkong, of course - to assess its viability to host the Games. But here's the rub. The Aussies might consider putting it around at the IOC's grandiose chateau HQ in Switzerland that frequent travellers to China must by law subject themselves to AIDS tests, an alarming prospect that might lead the pampered and expense account-linked worthies of the IOC to leave it out of the reckoning altogether. Should that be the case, Mr Sales could console himself by batting for Manchester. Apart from the political correctness of the choice (Mr Sales is, after all, the chairman of the Commonwealth Games Federation), the northern England city has so many Chinese inhabitants it could almost be a faraway province of mainland China. Besides, beef chow mein - No 47 on the menu of most Chinese takeaway establishments in Manchester - has now replaced pie-and-mushy peas as the local staple.