The Soviet grain harvest in 1988 was 195 million tons, the lowest for three years, a Soviet official announced Monday. The figure was considerably worse than Western experts had predicted. Stepan Sitaryan, first deputy chairman of the State Planning Committee, said the figure was preliminary. In 1987, Soviet farmers harvested 211.3 million tons while the figure for 1986 was 210.1 million tons. The target for 1988 was 235 million tons.