* Dry weather expected to slow U.S. spring wheat planting

* Corn supported by low ethanol stocks, continued exports

* Soy steady ahead of USDA supply and demand report

CHICAGO, April 8 (Reuters) - U.S. corn futures climbed on Thursday on export optimism and positioning ahead of the U.S. Agriculture Department's monthly supply and demand report, out Friday, traders said.

Wheat gained as frigid temperatures across Europe and the Black Sea region threatened crops. Soybeans were also firmer.

The most-active corn contract on the Chicago Board of Trade added 20-3/4 cents to $5.81-1/4 per bushel as of 12:30 p.m. (1830 GMT).

Chicago wheat was up 13-1/4 cents at $6.29-1/2 per bushel. Soybeans rose 8-1/2 cents to $14.17-1/4 per bushel.

Corn gained as the U.S. Energy Information Administration reported ethanol stocks at the lowest since November and as rain forecast for much of the U.S. Midwest threatened planting.

"We're only about a million gallons away from the October lows, in terms of stocks of ethanol, going into summer driving season," said Mike Zuzolo, president at Global Commodity Analytics.

Export sales of 757,000 tonnes of old-crop corn were reported by the USDA, down 5% from the week prior but in line with trade estimates.

"I think there could be a little bump in the December (contract) today with the thought that maybe we're not going to get this thing off to as fast a start as we thought," said John Zanker, market analyst at Risk Management Commodities.

Wheat rose as a cold spell this week in France, the European Union's top wheat grower, brought record temperature lows for April, tempering recent optimism about harvest prospects.

Soybeans struggled for direction ahead of the USDA's supply and demand report, underpinned by tightening stockpiles but capped by seasonally shifting exports.

The USDA reported net cancellations to old-crop U.S. soybean sales in its weekly report, while Brazil's ANEC export association said it expected a year-over-year jump in soy shipments this month. (Reporting by Christopher Walljasper; additional reporting by Gus Trompiz in Paris and Naveen Thukral in Singapore; Editing by David Evans)