GRAINS-Soy, corn hit new lows as trade war with China escalates

* U.S. new tariff plan vs Chinese goods unnerves investors

* Soybean seen as U.S. crop most exposed to China trade war

* Good crop conditions, weather also hit corn, soy, wheat (Rewrites throughout, adds quote, updates prices, changes byline, changes dateline from PARIS/SINGAPORE)

CHICAGO, July 11 (Reuters) - U.S. soybean futures dropped to contract lows on Wednesday as an escalating trade war with China stoked worries about long-term export demand from the world's top importer of the oilseed.

Favorable crop weather in the U.S. Midwest weighed on soybeans and corn, which also hit contract lows, on expectations for bumper harvests this season.

Wheat slumped for a third straight day, following corn and soy lower and as stiff global competition dented demand for U.S. shipments.

Worries about rising trade tensions with China hung over markets in general after Washington detailed products to be covered by a 10 percent tariff on an extra $200 billion worth of Chinese imports. China has vowed to strike back.

The hardening standoff has put particular pressure on soybeans, the most valuable U.S. agricultural export to China, which bought more than $12 billion of U.S. soybeans last year.

The president of state grains trader COFCO was quoted on Wednesday as saying China could reduce reliance on U.S. soybeans by increasing imports of soybeans from other countries, or other oilseeds, or meat directly.

"In the short-run, China's probably not going to be able to take too much of their business away from the U.S., and what they do likely will get displaced. But in the long run, this is giving them more incentive to develop other channels," said Ted Seifried, analyst with Zaner Ag Hedge.

Chicago Board of Trade August soybean futures fell 19 cents, of 2.2 percent, to $8.36-3/4 a bushel by 12:39 p.m. CDT (1739 GMT) after notching a contract low of $8.35-1/2. July 2018 through May 2019 all set new life-of-contract lows.

CBOT September corn touched a contract low of $3.40-1/2 a bushel and were down 6-1/2 cents, or 1.9 percent, at $3.41-1/4 a bushel. July 2018 through September 2019 contracts all hit fresh lows.

Forecasts for a favorable mix of rain and moderate heat in the week ahead in the U.S. Midwest has underscored the prospect of a bumper corn harvest and bolstered expectations that the U.S. Department of Agriculture (USDA) will raise its production forecast in a monthly crop report on Thursday.

CBOT September wheat futures fell 16 cents, or 3.3 percent, to $4.76 a bushel.

Generally favorable growing conditions for U.S. spring wheat anchored wheat prices, along with easing concern about global supplies.

France's farm office FranceAgriMer said on Tuesday the country had bigger wheat stocks than expected.

(Additional reporting by Gus Trompiz in Paris and Naveen Thukral in Singapore; Editing by Amrutha Gayathri, Mark Potter and Richard Chang)