GRAINS-Soy posts 10-year low on huge U.S. crop, China trade woes

* Most-active soybean futures fall to lowest since 2008

* Record U.S. crop, stalled Chinese demand drags down beans

* Corn to contract lows on soy's skid, U.S. harvest pressure

* Wheat futures firm, bucking weak trend

(Recasts with updated prices, quotes; changes byline, changes dateline from previous HAMBURG) CHICAGO, Sept 18 (Reuters) - U.S. soybean futures fell to life-of-contract lows on Tuesday and the most actively traded contract hit its lowest in a decade as an escalating U.S.-China trade war darkened U.S. export prospects, analysts said. Corn futures also hit contract lows as the U.S. harvest expanded, while wheat futures rose on tightening global supplies. As of 12:56 p.m. CDT (1756 GMT), Chicago Board of Trade November soybeans were down 7-1/4 cents at $8.16-1/4 a bushel after dipping to $8.12-1/4, a contract low and the lowest or a most-active soybean contract since December 2008. Soybeans sagged after Beijing added $60 billion of U.S. products to its import tariff list in retaliation for President Donald Trump's planned levies on $200 billion worth of Chinese goods. The tit-for-tat measures are the latest escalation in an increasingly protracted trade dispute between the world's two largest economies. China is by far the world's top soy consumer, while the United States is the No. 1 soybean producer. The U.S. harvest of corn and soybeans is underway, and the U.S. Department of Agriculture has projected record-high yields for both crops. "The (weakness in) beans especially is all about tariffs ... Meantime, we've got generally very solid yields," said Jack Scoville, analyst with the Price Futures Group in Chicago. After the market closed on Monday, the USDA said the U.S. soybean harvest was 6 percent complete, above the five-year average of 3 percent. U.S. corn harvesting was 9 percent complete, ahead of the five-year average of 6 percent, the USDA said. CBOT corn futures followed soybeans lower, with benchmark December corn down 4 cents at $3.44 a bushel after hitting a contract low of $3.42-1/2. Wheat bucked the weaker trend, with CBOT December wheat up 5 cents at $5.11-1/4. Wheat drew support from possible frost damage over the weekend in western Australia, as well as news that Russia's agriculture ministry projected 2018/19 wheat exports at 30 million tonnes, below the USDA's last estimate of 35 million.

Traders awaited the results of an international purchase tender by Egypt's main state wheat buyer. The cheapest offer was $226 a tonne (free on board) for 60,000 tonnes of Russian wheat, traders said.

CBOT prices as of 12:58 p.m. CDT (1758 GMT):

Net Pct Volume Last change change CBOT wheat WZ8 511.25 5.00 1.0 44903 CBOT corn CZ8 344.00 -4.00 -1.2 154089 CBOT soybeans SX8 816.75 -6.75 -0.8 71004 CBOT soymeal SMZ8 304.30 -1.40 -0.5 49395 CBOT soyoil BOZ8 27.42 -0.28 -1.0 40219

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

(Additional reporting by Michael Hogan in Hamburg and Naveen Thukral in Singapore; editing by Jason Neely and Tom Brown)