NUMEROUS FACTORS SAID POINT TO USSR CORN BUYING A greater than anticipated need, competitive prices and political motivations could be sparking Soviet interest in U.S. corn, industry and government officials said. As rumors circulated through grain markets today that the Soviet Union has purchased an additional 1.5 mln tonnes of U.S. corn, industry and government sources noted a number of factors that make Soviet buying of U.S. corn likely. First, there are supply concerns. Some trade sources said recent speculation has been that last year's Soviet grain crop be revised to only 190 mln tonnes, rather than the 210 mln announced, therby increasing the Soviet need for grain. A drop in Argentine corn crop prospects could also affect Soviet corn buying, an Agriculture Department source said. Dry weather in Argentina -- a major corn supplier to the USSR -- and reported crop problems prompted USDA to lower its Argentine 1986/87 corn crop estimate this week to 11.0 mln tonnes, down from 11.5 mln. Argentina corn exports were also cut by 500,000 tonnes to 6.8 mln tonnes. Argentina has already committed four mln tonnes of this year's corn for export, a USDA official said, with two mln tonnes of that booked for April-June delivery to the USSR. "Significant downside potential" still exists for the Argentine crop, the official said, which will decrease the amount of additional corn that country can sell to Moscow. "If the Soviet needs are greater than we have been thinking, then they might need more than what Argentina can provide during the April to June period," he said. Current competitive prices for U.S. corn have also sparked Soviet buying. U.S. corn was reported to be selling on the world market earlier this week for around 71 dlrs per tonne, Argentine corn for 67 dlrs -- a very competitive price spread, U.S. and Soviet sources said. "This price difference makes American corn competitive," Albert Melnikov, commercial counselor for the Soviet Union, told Reuters. Impending crop problems in Argentina will likely cause those prices to rise, and with the recently strong U.S. corn futures prices, the Soviets might feel corn prices have bottomed and that this is a good time to buy, sources said. Finally, some industry sources said that by buying the minimum amount of corn guaranteed under the U.S./USSR grains agreement (four mln tonnes), the Soviet Union may be hoping to convince the USDA to offer Moscow a subsidy on wheat. In an inteview with Reuters this week, USDA secretary Richard Lyng said that no decision had been made on a wheat subsidy offer, but that such an offer had not been ruled out.