(New throughout, updates prices, adds analyst comments; changes byline, dateline, previous PARIS/SYDNEY)
By Michael Hirtzer
CHICAGO, July 28 (Reuters) - U.S. corn and soybean futures fell 1 percent or more on Thursday, pressured by ample existing supplies and largely favorable growing conditions that will likely lead to huge harvests this fall, traders and analysts said.
Chicago Board of Trade corn futures led the declines, with technical selling weighing further after prices failed to rise above their 10-day moving average.
CBOT December corn futures eased 5-1/4 cents to $3.37-3/4 per bushel, heading for their largest daily losses since July 19. CBOT November soybeans were down 10 cents to $9.76 as of 1:02 p.m. CDT (1802 GMT), declining after rising the past two sessions.
U.S. Department of Agriculture weekly U.S. export sales for the current marketing season of a negative 1,400 tonnes of soybeans were below expectations for sales of 250,000 to 450,000 tonnes. Export sales of 438,800 tonnes of corn were within the range of estimates.
"The export sales were a little disappointing," said Ted Seifried, analyst at brokerage the Zaner Group.
Seifried added that some traders were betting the USDA will boost corn yield estimates in its monthly supply and demand report due on Aug. 12 due to historically high U.S. crop condition ratings.
Plentiful rain this summer has developing corn and soy crops in good shape, boosting yield potential. The Commodity Weather Group in a note to clients said showers expected during the next 15 days should aid much of the U.S. crops.
"Soybean plants are in an excellent condition so far," Commerzbank analysts said in a note. "Concerns about yield losses therefore seem overstated, particularly since the weather outlook can change again quickly."
Wheat futures also were lower but holding just above their nine-year lows from earlier this month. CBOT September wheat was down 5-1/4 cents at $4.09-1/2 per bushel.
Traders were awaiting final results due after the close of trading from a U.S. spring wheat tour in North Dakota that pointed to lower yields this year.
Additonal reporting by Colin Packham in Sydney and Gus Trompiz in Paris; Editing by David Evans and Dan Grebler