WASHINGTON — Corn rated good to excellent in the week ended Aug. 3 declined to 73% compared with 75% in the previous week, the U.S. Department of Agriculture said in its Aug. 4 Crop Progress report. Twenty per cent of the crop was rated fair, compared with 19% the previous week, and 7% was rated very poor to poor compared with 6% the previous week.

Soybeans rated good to excellent as of Aug. 3 remained at 71%, the same as the previous week. Also remaining at levels of the previous week were fair (23%) and very poor to poor (6%) ratings.

Crop observers were concerned that a turn to longer-term dry weather in much of the Corn Belt may lead to some deterioration in conditions of both the corn and soybean crops. Their expectations were borne out in the case of corn, but soybeans were holding at the same condition ratings of the previous week.

The key stage of silking, crucial in the corn pollination process, reached 90% complete in the 18 major states as of Aug. 3, compared with the five-year average of 88%. Thirty-six per cent of the crop had reached the dough stage as of Aug. 3 compared with a 29% five-year average.

August is considered the key month in determining the ultimate size and quality of a soybean crop. As the month unfolded, the U.S.D.A. said 85% of the crop in the 18 major states was blooming, compared with 83% as the five-year average. Fifty-seven per cent of the crop was setting pods in the latest week, compared with 48% as the five-year average for the date.

The harvests of hard red and soft red winter wheat crops in the 18 major states were 90% completed as of Aug. 3, compared with an 85% five-year average.

Spring wheat conditions in the six major states remained the same as the previous week, with 70% rated good to excellent, 25% fair and 5% very poor to poor. Ninety-seven per cent of the crop was headed as of Aug. 3, compared with 97% as the five-year average.

Fifty-six per cent of the oats crop in the nine major states was harvested as of Aug. 3 compared with 49% as the average. Conditions of the crop deteriorated modestly, with 63% of the crop rated good to excellent (64% the previous week), 25% fair and 12% very poor to poor (11%).