The Soviet Union and United States concluded a new grain pact Monday after eight months of difficult negotiations.

Soviet Foreign Ministry spokesman Gennady Gerasimov told a news conference Moscow would buy at least an annual nine million metric tons of grain and soya beans from the United States under the pact, which would run until December 31, 1990.In Washington a spokesman for Trade Representative Clayton Yeutter, Roger Bolton, said the pact was retroactive to Oct. 1, 1988, and terms were identical to those of a five-year grain pact that expired in September.

Bolton said export subsidy offers were not included in the grain pact.

Under the expired agreement, the Soviets were pledged to buy four million metric tons each of wheat and corn annually, plus an additional one million tons of grain or 500,000 tons of soybeans or soybean meal.

The grain was to be priced at prevailing market levels.

Bolton said the new pact was identical in its purchase requirement and pricing terms.

The pact, which came into force on October 1, was effectively a continuation of a five-year agreement between the two sides which expired in September.

Gerasimov said, "The agreeement provides for annual purchase of nine million tons of grain and soya beans and provides when necessary to buy additional amounts."

The Soviet spokesman said the two sides also agreed to hold talks on the prolongation of the deal beyond its expiration date.

As part of the protocol, the Soviet Union had already bought 5.5 million tons of corn and more than a million tons of soybeans for delivery in the 1988-89 agricultural year.