GERMAN RESEARCH INSTITUTE LOWERS GROWTH FORECAST The DIW economic research institute said West German economic growth in 1987 is unlikely to reach the 1.5 pct rate it had forecast earlier this year. The institute, whose forecasts are more pessimistic than those of the other four leading German institutes, said the economy had passed its peak in the summer of 1986, and its prospects had dimmed significantly since the autumn. The DIW repeated earlier predictions that gross national product (GNP) in the first quarter of 1987 would contract in real, seasonally adjusted terms against the weak final quarter of last year.