SPENDING on machinery and equipment in the third quarter of 1992 grew by 28.5 per cent, according to data released yesterday by the Census and Statistics Department. While overall economic growth figures - gross domestic product grew by 5.2 per cent in the third quarter - matched most economists' expectations, the investment numbers showed a strong trend towards labour replacement and productivity enhancement. While most of the news in Hongkong's latest economic performance figures was good, a 20.7 per cent surge in imports trimmed the territory's growth rate despite increases in real gross domestic fixed capital investment (up 11.8 per cent), real private consumption (up 9.1 per cent) and real Government expenditure (up 9.5 per cent). Mr Benjamin Chan, an economist at the Bank of East Asia, said Hongkong's export growth, new airport project and high profitability for most sectors were behind the spurt in investment. ''Investment sentiment is so good and people are continuing to consume,'' he said. ''We are looking for whole-year growth of five per cent.'' He warned, however, that Hongkong's expanding trade deficit would continue to contain growth. Hongkong Centre for Economic Research director Richard Wong predicted in a paper that should growth rates in Hongkong and the United States continue at their current rates (measured over the decade) the average citizen in the territory would earn more than his US counterpart by the year 2006. He said that because of the understatement of income in Hongkong it could reach the United States standard of living even earlier. ''With a little luck, Hongkong just might achieve a standard of living comparable to that of the United States even by the year 2001,'' he said.