GRAINS-Corn falls 4 pct after USDA data; soy, wheat also decline

* USDA raises U.S. corn ending stocks forecasts

* U.S. Midwest rains bolster crops, pressure prices

* Wheat sags after USDA raises new-crop stocks view

(New throughout; updates prices; adds quotes; changes byline; dateline previously PARIS/SYDNEY) CHICAGO, July 12 (Reuters) - U.S. corn futures fell 4 percent on Wednesday after the U.S. Department of Agriculture raised its U.S. old- and new-crop corn ending stocks forecasts more than most analysts expected. Wheat and soybeans followed corn lower, with rains in Iowa and Illinois this week adding pressure. Chicago Board of Trade September corn settled down 16-1/4 cents at $3.85-1/2 per bushel. August soybeans fell 8-1/2 cents at $10.20-3/4 a bushel, and September wheat fell 16 cents at $5.37 a bushel. Corn posted the biggest declines on a percentage basis after the USDA in a monthly report raised its forecasts of U.S. corn stocks at the end of the 2017/18 marketing year to 2.325 billion bushels, up from 2.110 billion in June and above an average of analyst estimates for 2.181 billion. "We still have such big carry-in stocks that even with lower acres, we're still in a pretty comfortable position," said Alex Norton, director of risk management with Beeson and Associates. The USDA also left its U.S. 2017 corn yield forecast unchanged at 170.7 bushels per acre. Some analysts had expected a reduction due to stressful hot and dry conditions in parts of the Midwest. "With the weather that we've had, I think the trade is anticipating the yields will be something less than what we have now," said Don Roose, president of U.S. Commodities. CBOT soybeans briefly turned higher after the USDA lowered its soy ending stocks forecasts for both the 2016/17 and 2017/18 marketing years. But welcome rains the last two days in Iowa and Illinois, the top two producers of corn and soybeans, pressured futures, along with updated midday forecast models calling for milder conditions in the Midwest. "A little bit more rain in the forecast is considered a little bearish for soybeans, after $1.40 (per bushel) run from its lows," said Brian Hoops of Midwest Market Solutions. Wheat fell after the USDA raised its forecast of U.S. 2017/18 wheat ending stocks to 938 million bushels, from 924 million in June, bucking most trade expectations for a decline.

The USDA lowered its estimate of U.S. 2017/18 all-wheat production to 1.760 billion bushels, down from 1.824 billion in June but above the average estimate of 1.748 billion. Some analysts expect the USDA to lower its estimate of the U.S. spring wheat crop in future reports given drought in the northern U.S. Plains. "It usually takes a few reports to get all the damage reflected in the numbers," said Dan Cekander of DC Analysis.

CBOT settlement prices:

Net Pct Volume

Last change change

CBOT wheat WU7 537.00 -16.00 -2.9 94071 CBOT corn CU7 385.50 -16.25 -4.0 195337 CBOT soybeans SQ7 1020.75 -8.50 -0.8 43340 CBOT soymeal SMQ7 336.00 -2.70 -0.8 22777 CBOT soyoil BOQ7 33.52 -0.29 -0.9 39844

NOTE: CBOT September wheat, September corn and August soybeans shown in cents per bushel, August soymeal in dollars per short ton and August soyoil in cents per lb.

(Additional reporting by Colin Packham in Sydney and Gus Trompiz in Paris; Editing by Pritha Sarkar and Leslie Adler)