* CBOT wheat dropped 2.1 percent while Kansas City Board of Trade hard red winter wheat fell 2.2 percent. * MGEX spring wheat was down less than 1 percent as declines were limited by tight cash supplies. * CBOT volume was light, with less than 56,000 contracts changing hands. * Analysts were expecting the US Agriculture Department's weekly report on Thursday morning to show export sales of wheat between 450,000 to 650,000 tonnes compared with 503,000 tonnes last week. * Rosario Grains Exchange forecast Argentina's 2011/12 wheat crop was forecast at 12.8 million tonnes, up from the previous outlook for 12.4 million tonnes. * Tunisia tendered to buy 137,500 tones of optional-origin soft milling wheat, European traders said. * Syria bought 100,000 tonnes of Black Sea region wheat, likely from Romania, for 214.50 euros a tonne, European traders said.