Indications that the Brazilian soybean crop may be larger than expected sent U.S. soybean futures prices down modestly Thursday on the Chicago Board of Trade. Grain futures closed mixed to lower. Soybean futures opened lower on news that rain had eased dry conditions in the soybean-growing region of Brazil. Later in the morning, the Brazilian Institute of Geography and Statistics estimated the impending harvest would yield 19.4 million metric tons, significantly higher than the U.S. Agriculture Department's latest estimate of 18.5 million metric tons. ``This estimate was obviously negative for the U.S. market, and it took off any rallying attempt the beans might have had,'' said Walter Spilka, an analyst in New York for Smith Barney, Harris Upham & Co. Grain and soybean futures also retreated in reaction to generally lower prices for other commodities, Spilka said. Losses in corn were limited by expectations of new Soviet purchases, he said. At the close, wheat was 2 cents lower to 1 cent higher with the contract for delivery in March at $3.18 a bushel; corn was unchanged to { cent lower with March at $1.98{ a bushel; oats were { cent lower to } cent higher with March at $1.90} a bushel; soybeans were 1{ cents to 3\ cents lower with March at $6.22 a bushel.