WASHINGTON (AP) _ U.S. farm export volume hit a 6-year peak of 147.5 million metric tons in the year ended Sept. 30, with Japan again the biggest customer, the Agriculture Department said Monday.

In dollar terms, U.S. agricultural exports climbed from $27.87 billion in fiscal 1987 to $35.2 billion this past year, a gain of 26 percent, while imports of farm products were up 2 percent to a record $21 billion, USDA said.

That left the United States with a net agricultural trade surplus of $14.2 billion in black ink for fiscal 1988, compared with $7.22 billion a year earlier.

Export volume rose 14 percent from the 129.2 million metric tons posted in fiscal 1987, with wheat accounting for two-thirds of the increase, USDA said.

A metric ton is equivalent to about 2,205 pounds.

Wheat exports climbed from 28.2 million metric tons in 1987 to 40.5 million tons in the last fiscal year. The Soviet Union and China together purchased a total of 14.6 million tons of that amount, or 36 percent of all U.S. wheat shipments in fiscal 1988.

The Soviet Union and China together imported 4.95 million metric tons of American wheat, or 18 percent of total shipments, in 1987.

Japan led all customers, importing 27.8 million metric tons of U.S. agricultural goods. Other leading purchasers were: the European Community, 25.5 million metric tons; the Soviet Union, 15.9 million metric tons; South Korea, 8 million; and Taiwan, 7.3 million.

In addition to wheat, considerable tonnage gains were posted by corn, grain sorghum, feeds and fodders and vegetable oils. Among products not measured on the basis of metric tons, the biggest gains were in baby chicks, live animals, fruit juices, wines and malt beverages.

The surging gains, however, were moderated a bit by weakened foreign demand for U.S. soybeans, soybean meal and rice.

The Agriculture Department said all leading foreign markets grew in fiscal 1988 except that of the European Community, whose imports of U.S. agricultural goods dropped nearly 1.1 million metric tons. The decrease mainly reflected fewer purchases of soybean and soybean meal.

Indeed, the Soviet Union and Japan were among the five fastest-growing markets for U.S. agriculture, joining China, Algeria and India.

On the dollar value side, American high-value exports such as livestock and horticultural products climbed to a record $16.4 billion in 1988, a gain of $2.7 billion or 19 percent over the 1987 level. It also represented a $1.1 billion gain over the previous peak, reached in 1981.

Exports of bulk commodities shot up 33 percent from 1987 to a total of $18.8 billion. The level topped $25 billion in 1984 before immense crop surpluses and stiffer foreign competition battered prices and sent American agriculture into the doldrums.

Increased purchases of wheat and corn were the main reason for the increase, USDA said. It said the Soviet Union, China and North Africa were the leading markets for wheat and Japan, while the Soviet Union and South Korea were tops for corn.

Agricultural imports of $21 billion were some $250 million or 2 percent above the 1987 level and about $100 million over the 1986 mark of $20.9 billion, the previous record high. USDA said the increase was not limited to any single commodity group but instead reflected modest increases in nearly all major competitive items.

Top suppliers were: the European Community, $4.12 billion; Canada, $2.37 billion; Mexico, $1.9 billion; Brazil, $1.9 billion and Australia, $1.15 billion. Products reflecting increases were vegetable oil, live cattle, beef and veal, wines and malt beverages and nursery products.

There were drops in imports of sugar, pork, fur, coffee and spices.

802EST