GRAINS-Corn slips as U.S. crop rating improves, wheat also retreats

* Corn falls as USDA reports improved crop condition

* Forecasts of rains in coming days seen boosting corn, soybeans

* Wheat falls, giving up Monday's gains (Adds comment, detail, changes byline, adds LONDON dateline)

LONDON/SINGAPORE, Aug 15 (Reuters) - Chicago corn futures retreated on Tuesday as better crop conditions and forecasts for more rain across the U.S. Midwest boosted expectations for a bumper crop.

Wheat also slid, giving up last session's gains as ample supplies kept prices under pressure.

The Chicago Board Of Trade most-active corn contract was down 1 percent at $3.72-1/2 a bushel by 0932 GMT, giving up gains from the previous day when prices edged up 0.4 percent.

Soybeans fell 0.4 percent to $9.34-1/2 a bushel, hovering above lows touched on Monday. Wheat also lost 0.79 percent, falling to $4.37-1/2 a bushel.

December wheat futures on Euronext were down 0.46 percent at 162.75 euros a tonne.

"Weather forecasters have a fairly corn-friendly outlook for the next week or so," said Tobin Gorey of the Commonwealth Bank of Australia. "And corn crop conditions for last week were a little better, according to the USDA's survey."

After the market closed on Monday, the U.S. Department of Agriculture said 62 percent of the corn crop was in good to excellent condition, up 2 percent from last week. Analysts had expected the crop to be pegged at unchanged.

The USDA report eased concerns about potential production losses due to a recent bout of dry weather.

The agency pegged the soybean crop at 59 percent good to excellent, down 1 percent from the previous week and behind market forecasts for unchanged.

Rainfall this week is also expected to further benefit crops. About 70 percent of U.S. corn and soybean growing areas should receive rains in the next five days, according to forecasts by the Commodity Weather Group.

Meanwhile, U.S. soybean suppliers are expected to face stiff competition from Brazil where exports so far this year have exceeded volumes for all of 2016 as the country harvests a bumper crop, according to preliminary data from the Development Ministry.

Up until the second week of August, Brazil, the world's largest exporter of the oilseed, had sold 53.37 million tonnes, almost 3.5 percent above exports for the whole of last year, according to government data.

The National Oilseed Processors Association's monthly report had been expected to show that the pace of soybean crushing in the U.S. eased slightly in July from a year earlier.

Analysts were expecting a July crush of 143.004 million bushels, according to the average of five estimates in a Reuters survey. NOPA reported a crush of 143.715 million bushels for July 2016. (Reporting by Ana Ionova in London and Naveen Thukral in Singapore; Editing by Richard Pullin and Susan Thomas)