The huge losses to 1988 harvests came mostly in June and July, when drought and searing heat shriveled corn and soybean yields across much of the nation, new Agriculture Department estimates show. Assistant Secretary Ewen M. Wilson, the department's chief economist, said total grain production this year is expected to drop to 191 million metric tons, down 31 percent from 1987. Total supplies of grain for 1988-89, which include inventories at the beginning of the season, are forecast at 366 million tons, down 24 percent from last year. Wilson said at a news conference Monday that ``crop development now has progressed to the point where production can be forecast with a reasonable degree of confidence.'' The corn yield, for example, was estimated at 78.5 bushels per harvested acre, down from 119.4 bushels last year, the largest drought-induced reduction in yield on record, he said. From 1965 to 1987, the September estimate overstated corn production on nine occasions and understated it on 14 occasions, Wilson said. In the case of soybeans, the September estimate overshot final production in 12 years and understated it in 11. Wilson said rainfall in the last month ``has improved the conditions of pastures and ranges, although more precipitation is needed to restore them to normal.'' Wilson said he is holding to an earlier prediction that consumer food prices will go up an average of 3 percent to 5 percent this year, with about 1 percent of the rise caused by drought. A further increase is expected in 1989. The new USDA estimates showed the corn harvest, which is under way, is expected to be at a five-year low of 4.46 billion bushels, down 37 percent from 7.06 billion bushels harvested in 1987. Even so, that was down by less than 1 percent from the forecast a month ago. In May and June, before the drought tightened its grip, USDA projected the corn harvest at 7.3 billion bushels, based on trends and an assumption of normal weather. Those projections were revised downward in July to 5.2 billion bushels, assuming farmers got normal weather the remainder of the season. In August, the forecast was lowered to 4.48 billion bushels, the smallest harvest since 1983, when drought and federal acreage curbs reduced output to 4.17 billion bushels. The soybean harvest was estimated at a 12-year low of 1.47 billion bushels, down 23 percent from 1.9 billion bushels produced last year but virtually unchanged from the August forecast. Estimates last spring called for about 1.88 billion bushels, and the July projection was 1.65 billion bushels. Production of all wheat was projected at 1.81 billion bushels, down 14 percent from 2.1 billion produced in 1987 and 1 percent below the August forecast. In May and June, USDA forecast this year's wheat output would be up slightly. The July projection was 1.84 billion bushels, and the August forecast was 1.82 billion bushels. Corn is the largest and most important crop grown by American farmers and, as a feed ingredient, is essential to the production of meat, poultry and dairy products. Soybeans, which provide high-protein meal and quality vegetable oil used in food processing, also are vital to U.S. food production. No new estimate of winter wheat production was included. Last month's forecast, which was carried forward into the September report, was 1.55 billion bushels, down 1 percent from last year. New estimates for spring planted wheat included durum, 49.2 million bushels, down 47 percent from 1987 production and the smallest harvest since 1961. The new estimate was also down 10 percent from August. Other spring wheat was estimated at 206 million bushels, down 54 percent from last year and 3 percent below the August forecast. Cotton production was estimated at 14.7 million bales, down 2 percent from August but only slightly below the 1987 crop. The crop was projected at 13.7 million bales in July. Overall, the department's Agricultural Statistics Board said U.S. crop production this year is expected to drop to 88 percent of a 1977 base used as a comparison. That would be the lowest since 1983. Crop production last year averaged 106 percent of the base year. The record was 117 percent reached in 1985, 1982 and 1981.