(Recasts, updates with U.S. trading, adds new analyst quote, details; changes byline, dateline, pvs PARIS/SINGAPORE)
By Mark Weinraub
CHICAGO, Aug 18 (Reuters) - U.S. soybean futures eased 1.6 percent on Thursday, retreating from a recent export-driven rally amid technical sales and huge crop expectations, traders said.
Wheat and corn futures also weakened, but short-covering limited the sell-off in grains as investors unwound bearish bets.
Rain in key U.S. growing areas that removed some lingering doubts about crop development also contributed to the weakness in soybeans.
"We have got some weather moving through the Midwest that is finishing up the bean crop," said Dan O'Bryan, a risk management specialist and broker at Top Third Ag Marketing.
At 10:36 a.m. CDT (1536 GMT), Chicago Board of Trade November soybean futures were down 16-1/4 cents at $9.99-3/4 a bushel.
Soybean prices firmed slightly during overnight trading to a four-week high, but a wave of technical selling pushed prices lower after the November contract failed to break through the high end of its 20-day Bollinger range, a level it has traded below since June 13.
Before weakening on Thursday, soy futures had notched a 5.7 percent rise since Aug. 12, when the U.S. Agriculture Department issued a forecast for a record U.S. harvest. A slew of fresh export deals muted the impact of the production outlook during the rally.
But USDA's weekly export report on Thursday morning came in as expected and did not provide the fresh fuel that traders said the soy market needed to spur more gains, traders said. The report showed old-crop export sales in the latest week totaled 177,900 tonnes and new-crop export sales 1.598 million tonnes.
Corn was consolidating after a four-session rally that had seen the cereal recover from a seven-year lows. USDA also issued a forecast for record corn production last week.
Wheat also ticked lower as the market remained capped by big harvests in exporting countries in North America and the Black Sea region.
CBOT December corn futures were 2 cents lower at $3.37-3/4 a bushel and CBOT September wheat was off 1/4 cent at $4.25-3/4 a bushel.
USDA's export sales report showed that old-crop corn sales in the latest week were 167,400 tonnes, below market forecasts. New-crop corn export sales of 1.043 million tonnes were in line with expectations.
For wheat, USDA said export sales totaled 489,500 tonnes, matching trade forecasts. (Additional reporting by Naveen Thukral in Singapore and Gus Trompiz in Paris; Editing by Joseph Radford, Adrian Croft and W Simon)