The blistering summer drought, in combination with the administration's crop-reducing payment-in-kind (PIK) program, will push U.S. corn and soybean harvests to their lowest levels in years, the Department of Agriculture predicted yesterday.

In its first official estimate of the 1983 crop, the USDA said data available as of Aug. 1 indicated that the corn harvest will be 38 percent below last year's record crop and the soybean harvest will be down 19 percent.

But Deputy Secretary of Agriculture Richard E. Lyng warned that the dry, torrid conditions that have continued since Aug. 1 in the major farming areas could reduce corn and soybean production even further. This would be certain to increase meat prices, although not until next year at the earliest.

The drought has pushed up prices for the grains that farmers feed their cattle, hogs and chickens. Soybeans, for example, have climbed roughly $3 per bushel since April to a profitable level of about $8.50. Corn has increased about $1 per bushel since last winter.

Livestock industry analysts say the higher production costs will lead to a reduction of herd sizes and a tightening of meat supplies, resulting in higher prices to consumers.

Yesterday's crop forecast, Lyng said, "is not the final word by any means." He said that he expects that the USDA would scale down its crop forecast even more next month because of the continuing heat and lack of rain at a crucial time for corn and soybean formation.

"But the main point is that even though there is substantial damage due to weather, the big corn carryover will give us clearly what appears to be an ample supply for domestic needs and exports," Lyng said.

While supplies will be ample, Lyng said, the continuing drought could deal "a severe blow" to many farmers. "It is going to be a serious problem, particularly for individual producers," he said.

The drought comes at a time when the Reagan administration is overseeing the largest crop reduction program in history in an effort to reduce farm surpluses created by record-breaking harvests in 1981 and 1982.

The PIK program, giving farmers surplus grain in return for their not planting this year, was expected to cut the corn crop to about 6.2 billion bushels from last year's 8.4 billion bushels. USDA forecasters said yesterday that the disastrous July weather would cut corn by an additional 1 billion bushels.

The USDA said that soybean production would be 1.84 billion bushels, almost a fifth less than last year and 8 percent lower than the 1981 crop, due to weather stress and the smaller acreage. The forecast said that yields would be 29.7 bushels per acre, compared with 32.2 last year.

Corn, in contrast, will be more severely affected by the drought. This year's yield is projected at 99.9 bushels an acre, down from last year's 113.9 bushels, with Illinois and Indiana averages down by 32 and 37 bushels per acre, respectively.

The forecast also said the wheat crop will be down 14 percent, cotton will be down 35 percent and hay will be down 5 percent from last year's record yields for all three commodities. Sorghum will be down 33 percent and rice down 31 percent.