American rice farmers may benefit in the early months of the 1988-89 season from a shortage of exportable crops in competing nations, an Agriculture Department report said Friday. World rice production from the 1987-88 harvests is forecast at 304 million metric tons, milled equivalent, down 4 percent from last year, the department's Economic Research Service said. Weak monsoons left Asian producers with limited supplies. Meanwhile, global rice consumption is expected to increase 3 percent, leaving world stockpiles at their lowest level relative to use since 1974. The U.S. rice supply also has tightened, reflecting a 6 percent reduction in last year's harvest. But the department's planting survey in early March indicated American producers intend to boost 1988 rice plantings by 19 percent to 2.8 million acres. That could boost this year's output sharply. ``U.S. farmers will harvest rice crops at least four months ahead of their Asian competitors,'' the report said. ``Since the United States will be the major source of supply during those months, some increased export opportunities may exist towards the end of 1988.'' However, analysts cautioned that some foreign importers, if possible, may ``choose to wait until the beginning of 1989, when prices are likely to decline during the Asian harvest.''