CHICAGO, June 5 (Reuters) -

Chicago Board of Trade corn and soybean futures fell on Monday, retreating from gains made during the overnight trading session on signs that already light export demand for U.S. supplies had weakened further, traders said.

Wheat futures were firm, with the biggest gains being notched by K.C. hard red winter wheat and MGEX spring wheat contracts due to tight global stocks of high protein offerings.

Corn futures posted the biggest declines, sinking nearly 2% as traders shrugged off the potential impact that hot and dry weather in the U.S. Midwest might have on the recently seeded crop.

"I think we are still early enough that it is not irreversible damage being done yet," said Mark Schultz, chief market analyst at Northstar Commodity. "The biggest thing is that there is nothing on the demand side."

The U.S. Agriculture Department said on Monday that weekly export inspections of corn fell to

1.180 million tonnes

from 1.346 million tonnes the prior week.

At 11:08 a.m. CDT (1608 GMT), CBOT July corn futures were down 11 cents at $5.98 a bushel. The contract hit a six-week high before turning lower.

CBOT July soybean futures were down 1-1/2 cents at $13.51 a bushel.

Soybean export inspections were reported at 214,247 tonnes, down 11.9% from a week earlier.

CBOT July soft red winter wheat was up 2-3/4 cents at $6.21-3/4 a bushel.

Wheat futures also garnered support from uncertainty about a deal allowing for shipments from Ukraine's Black Sea ports, as well as signs of a pick-up in global demand for wheat following recent price declines.

Russia's foreign ministry said on Monday that it saw no prospects for extending the Black Sea grain export deal, which is set to expire in mid-July, Russian news agencies reported.

Saudi Arabia bought 624,000 tonnes of wheat in a tender on Monday, more than the 480,000 tonnes sought, with traders expecting Black Sea wheat, especially Russia's, to be heavily supplied. (Additional reporting by Michael Hogan in Hamburg and Naveen Thukral in Singapore, Editing by Kirsten Donovan and Paul Simao)