ALSO OF NOTE IN USSR

Moscow's recent agreement to an extension of a grain-purchase accord with the Americans has come against the background of indications the Soviet Union is headed for its fourth dissappointing harvest in a row.

The official Soviet news media have carried a series of reports on weather damage to this year's crop.

For instance, a report Aug. 16 said the harvest in the key grain-producing republic of Kazakhstan promised to be ''one of the most difficult in recent years. The early spring and the subsequent cold spells affected the growth and ripening of the plants. Hardly a drop of rain fell during the tilling of the wheat.''

Still, the Soviets are signaling displeasure over US trade policy by moving to purchase an ever-larger proportion of their grain imports from outside the United States, particularly from Argentina, Canada, Australia, and Brazil.

Under present agreements, Brazil, for instance, is to export 500,000 tons of soya beans to the Soviet Union each year until 1986. But a deputy Soviet trade minister, on a recent visit to Brazil, said Moscow was ready to hike soya imports to between 2 and 3 million tons annually.