* Soybean futures reach two-year high
* Corn, wheat retreat from recent gains
* USDA cuts estimates for Brazil soy, corn harvests (New throughout, updates prices, market activity and analyst comment to close, adds details about fund activity)
By Tom Polansek
CHICAGO, June 10 (Reuters) - U.S. soybean futures rose for the ninth straight week, the longest bull run in 43 years, on expectations that crop problems in Brazil and Argentina will steer more export business to the United States.
The U.S. Department of Agriculture (USDA) confirmed increased demand in a monthly crop report that raised the government's estimate for soybean shipments and tightened its outlook for domestic supplies more than expected.
"Nothing on today's report undermines bull soy narrative," said Rich Feltes, head of market insights for broker RJ O'Brien.
July soybeans ended 0.2 percent higher at $11.78-1/4 per bushel on the Chicago Board of Trade and reached the highest price for a most-active contract since June 2014. The last time soybeans rose for nine weeks in a row was in 1973.
For the day, July corn slipped 0.8 percent to $4.23 a bushel. The contract reached its highest point since July 2015 on Wednesday. July wheat lost 3 percent to $4.95 a bushel. On Wednesday, it set its highest price since November 2015.
The sector has had a roller coaster year. In January, grain prices careened toward multi-year lows and the U.S. dollar was at a demand-dampening 12-year high against other currencies.
Recently, the market has swung violently in the other direction, as a severe drought has hit Brazilian corn production while heavy rains have swamped Argentina's soy crop.
The USDA, in its crop report, trimmed its estimate for the 2015/16 Brazil corn harvest by 3.5 million tonnes to 77.5 million tonnes and for the Brazil soy harvest by 2 million tonnes to 97 million tonnes.
"The South American crops are getting smaller, not larger," said Karl Setzer, risk management team leader for MaxYield Cooperative in Iowa.
Supporting the rally were two private sales of U.S. soybeans to unknown destinations, which the USDA announced separately from its crop report.
Commodity funds bought an estimated net 9,000 soybean contracts and sold about 9,000 corn contracts and 7,500 wheat contracts at the CBOT, traders said.
Traders will focus now on what the USDA will say on June 30, when it releases its estimates for U.S. quarterly grain stocks and planted acres. They also will keep a close eye for weather that could threaten recently planted U.S. corn and soybean crops.
Additional reporting by Nigel Hunt in London and Naveen Thukral in Singapore; Editing by Phil Berlowitz and David Gregorio