* USDA cuts U.S. corn yield, production; soy crop unchanged
* Concerns about interim China trade deal weighs on soy
* Wheat retreats as global supply seen rising (Rewrites throughout with U.S. market open, adds quote, updates prices, changes byline, changes dateline from PARIS/SINGAPORE)
CHICAGO, Nov 8 (Reuters) - U.S. corn futures firmed on Friday after the U.S. Department of Agriculture lowered its U.S. yield and harvest forecasts in a monthly crop report, though gains were kept in check by worries about weak demand.
Soybeans fell as the USDA left its U.S. crop yield and harvest outlooks unchanged despite poor weather this summer and fall that had many market observers expecting cuts.
The forecast, in a monthly USDA crop supply-and-demand report released at midsession, added to earlier pressure stemming from renewed concerns about an interim U.S. trade deal with China.
Wheat briefly traded higher in tandem with corn but retreated as the USDA's cuts to U.S. and southern hemisphere production were more than offset by larger crops in the EU and Black Sea region.
The USDA forecast corn production of 13.661 billion bushels, based on an average yield of 167.0 bushels per acre (bpa). Analysts had been expecting production to fall to 13.643 billion bushels, and a yield of 167.5 bpa.
The agency pegged the soy crop at 3.550 billion bushels, with yields seen at 46.9 bpa, unchanged from October.
"There's nothing in this report that's friendly to the corn at all," said Brian Hoops, Midwest Market Solutions.
"We were negative going into the report and so now we're seeing a little bit of a relief bounce. But from a longer term standpoint, there's very little reason to think that corn is going to begin an up-trend in this market."
Chicago Board of Trade (CBOT) December corn was up 1-1/2 cents at $3.76-3/4 a bushel at 12:50 p.m. CST (1850 GMT). If the gain holds, the modest gain would be the contract's first price increase in seven sessions.
January soybeans fell 7-1/2 cents to $9.29 a bushel, while CBOT December wheat dropped 3-1/2 cents to $5.09 a bushel.
Renewed concerns about an interim U.S.-China trade deal weighed on the market ahead of the report, particularly soybeans.
President Donald Trump on Friday said he has not agreed to rollbacks of U.S. tariffs sought by China, sparking fresh doubts about when the world's two largest economies may end a 16-month trade war that has slowed global growth.
Earlier on Friday, the USDA confirmed private sales of 270,000 tonnes of U.S. soybeans and 217,040 tonnes of corn to undisclosed buyers via its daily export sales reporting system. Large soy purchases reported for unknown buyers are often assumed to be bound for China.
(Additional reporting by Gus Trompiz in Paris and Naveen Thukral in Singapore; editing by Giles Elgood and Steve Orlofsky)