GRAINS-Soybeans set for 4th weekly gain as USDA yield surprise fades

* Export demand, S. America weather risks boost soy prices

* Soy market looks beyond increased USDA harvest forecast

* Wheat set for weekly gain, big supplies seen priced in

* Corn lower after USDA yield rises

(Updates with European trading, changes byline/dateline) PARIS/SINGAPORE, Sept 15 (Reuters) - Chicago soybeans eased on Friday but stayed on course for a fourth straight weekly gain, as strong export demand and adverse weather in South America took attention away from a higher-than-expected government forecast for the U.S. harvest. Corn edged down to remain lower over the week, pressured by the U.S. Department of Agriculture's increased yield estimate on Tuesday, but concern over weather for South American planting also underpinned the market. Wheat ticked lower but was set for a weekly rise after a wave of short-covering that suggested investors had priced in large global supplies, with southern hemisphere crop risks encouraging the change in sentiment. The Chicago Board of Trade most-active soybean contract was down 0.4 percent at $9.71-3/4 a bushel by 1151 GMT. Over the week, it was up 1 percent after hitting a one-month high of $9.78-1/4 on Thursday. CBOT corn was down 0.4 percent at $3.52-3/4 a bushel, leaving it about 1 percent lower over the week. Wheat was 0.3 percent lower on the day at $4.41-1/2 a bushel but was up nearly 1 percent this week. "The market is discussing dry conditions in Brazil where soybean planting will begin next month," said Tobin Gorey, director of agricultural strategy at Commonwealth Bank of Australia. Torrential rain in Argentina was also raising doubts about the upcoming soybean and corn planting campaigns. In the United States, analysts were also cautious about the USDA's increased yield outlook and waiting for the start of harvesting for further clues as to the impact of dry weather. Brisk export demand has also lent support to soybean prices. The USDA reported export sales of U.S. soybeans in the latest week at 1.6 million tonnes, topping a range of trade expectations for 1.0 million to 1.3 million tonnes. Separately, the agency said private exporters sold another 198,000 tonnes of U.S. soybeans to China. In wheat, traders have pointed to a bottoming out in prices despite large global supplies. "The pessimism that market participants have already been displaying for months explains why the wheat price is faring well nonetheless expectations were already priced in," Commerzbank analysts said in a note. The shift in attention away from high inventories has been encouraged by the heavy rain in Argentina and reduced forecasts for the harvest in fellow southern hemisphere exporter Australia. Flooding last weekend in Argentina could cause a loss of 70,000 hectares of wheat plantings, out of a total 5.35 million hectares planted with the grain in the 2017-18 season, the Buenos Aires Grains Exchange said on Thursday.

Prices at 1151 GMT

Last Change Pct End Ytd Pct Move 2016 Move CBOT wheat 441.50 -1.50 -0.34 408.00 8.21 CBOT corn 352.75 -1.50 -0.42 352.00 0.21 CBOT soy 971.75 -4.25 -0.44 1004.00 -3.21 Paris wheat Dec 162.25 -1.00 -0.61 175.00 -7.29 Paris maize Nov 157.50 -0.50 -0.32 170.00 -7.35 Paris rape Nov 367.75 -0.50 -0.14 383.25 -4.04 WTI crude oil 50.03 0.14 0.28 53.72 -6.87 Euro/dlr 1.20 0.00 0.29

Most active contracts - Wheat, corn and soy US cents/bushel, Paris futures in euros per tonne

(Reporting by Naveen Thukral in Singapore and Gus Trompiz in Paris; Editing by Sunil Nair and Elaine Hardcastle)