P122 CEEFAX 122 Wed 29 Dec 13:18/32       US CUTS GROWTH FORECASTS  President Reagan's economic advisers have cut back their forecast for US economic growth in 1983 and are now predicting slow expansion in the first half of next year. A report in the New York Times s!ys they now expect a real increase in gross national product (GNP) of less than 2pc in 1983, compared with the 3.1pc rise predicted in September. The US unemployment rate, which reached a 40-year high of 10.8pc in Novjm"jr, is unlikely to show much reduction "y the end of 1983.  WALL STREET REPORT 127 