ONE of Hong Kong's top scientists says the Government should spend $2 billion a year on key technologies in the territory that would help the developing world, as a way of giving foreign aid. Professor Jeffrey Wong Tze-fei, director of the Biotechnology Research Institute at the Hong Kong University of Science and Technology (HKUST), said at a conference held at the weekend that as Hong Kong's gross national product (GNP) per person was now greater than that of Britain, ''it's time we thought about foreign aid''. Hong Kong's GNP per head was estimated at about $145,000 in the first half of the year, against $141,000 in Britain. Under the Basic Law, Hong Kong is unable to set foreign policy or give money in foreign assistance. Instead, Professor Wong suggests that the Government should spend the equivalent amount on technological research in the territory that would benefit less-developed nations. Biotechnology - the manipulation of proteins and genes, usually to attack diseases in animals or plants - could provide cures for illnesses such as hepatitis B, malaria and AIDS that plague Third World countries. As Hong Kong's population was roughly one-tenth of Britain's, it should spend about 10 per cent of what Britain spent, which would be about $2 billion, he told delegates at a seminar on Biotechnology and Ethics organised by the Baptist College and HKUST. As one of four key research priorities pinpointed by the Government, he said biotech would then receive $500 million a year, which would make ''a great difference in Hong Kong''. He pointed out that $300 million spent as a one-off by the Royal Hong Kong Jockey Club had set up his institute and its counterpart, the Hong Kong Institute of Biotechnology at the Chinese University. Many scientists regard biotech as the world's best potential weapon against deadly diseases such as AIDS. Experts estimate that developing countries will shoulder 90 per cent of the world's AIDS cases by 2000. And biotech could improve crop yield and protect plants from viruses that could kill up to 30 per cent of farmers' stocks in areas where people rely on such crops for survival. Professor Wong believes Hong Kong should help poorer nations in Asia and Africa to develop their own drugs, as the huge Western multi-national companies either cannot be relied on to provide cures for tropical diseases, or the drugs they produce are too costly for poor countries. For example, because of the huge costs of developing drugs and getting safety approvals, tissue plasminogen activator, a US drug hailed for its efficacy in clearing blood clots and saving people from death from heart attacks, now costs between $7,000 and $15,000 for a single dose. ''Biotech of this kind is really a spectator sport for Third World countries,'' he said. What he suggests is ''barefoot biotech'' - an affordable, home-grown form of the expensive American-style drug developments. For instance, silkworms are used in China to produce more cheaply the same drugs that US firms make in huge fermenters. But he warned small biotech set-ups to beware of predatory Western giants that could swallow a small group or its achievements. As an example, he cited a breakthrough made several years ago at the Shanghai Institute of Biochemistry. ''For the good of mankind, the Chinese had published the results'' of their work, showing an easy way to make insulin needed by diabetics. The Western firms adopted the method and made a fortune. ''There is no monopoly on human talent [in the West]. But the Third World must plan how to do the business. We can't afford to keep handing things over to multinationals,'' he said. The three other areas chosen by the Government for research focus are: information technology, new materials research and environmental technology.