INDIA will overtake China as the world's most populous country sometime in the first half of the next century, according to a United Nations report. The executive director of the United Nations Population Fund, Dr Nafis Sadik, said yesterday she expected India to overtake China in about the year 2020. The report, ''The State of the World Population'', published yesterday, puts China's current population at 1,205.2 million, growing to 1,539.8 million by the year 2025. Praising China's efforts to control its population growth, Dr Sadik said at a London news conference that the country had controlled its growth rate not so much by the one-child policy but through sound birth control education and the fact that women had been given much greater status within society. In 1949, Chinese families averaged six in size. That figure was already down to three by 1979, the year the one-child policy was introduced. ''[Population growth] came down because they provided access to family planning education and made it possible for women to make their own decisions on this,'' Dr Sadik said. China's cities are currently growing at a rate of 4.4 per cent a year, but only 28 per cent of the population can be classed as living in urban areas, according to the report. India's current population is put at 896.6 million. While some projections put the population in India at 1,393.9 million by the year 2025, Dr Sadik believes it will actually have overtaken China by then. Life expectancy in China is put at 71 compared to 78 in Hong Kong. China's population growth rate currently stands at 1.4 per cent a year, while Hong Kong's growth rate, at 0.8, is the same as that in South Korea and higher than Japan, where it is 0.4 per cent. Hong Kong's population is put at 5.8 million today, growing to 6.4 million by 2025. A United Nations conference on a plan of action to control population growth will be held in Cairo next month.