The value of U.S. agricultural exports rose to a nine-year high in the fiscal year that ended Sept. 30, but Agriculture Department analysts say it'll be tougher sledding in 1991.

In fiscal 1990, the department's Economic Research Service said export values rose to $40.2 billion from $39.7 billion in 1989. That was the most since the record of $43.8 billion in 1981.Bumper crops in some other countries have already lowered prospects for U.S. grain exports in the coming year, the report said.

For example, the export volume of corn in September - the final month of the 1990 fiscal year - plunged to 2.7 million metric tons, the lowest monthly volume since February 1987.

Although analysts were not specific on the effects of an export slowdown, the report noted other factors that will have a bearing on farm income in 1991 and beyond.

"The U.S. economy continues to grow very slowly, and the outlook is for more slow growth, or even a brief contraction," the report said.