CHICAGO, July 30 (Reuters) - U.S. corn futures were little changed on Thursday, hovering just above one-month lows, as benign crop weather and expectations of a large harvest overshadowed news of massive U.S. corn sales to China, analysts said.

Soybean futures were modestly higher while wheat futures drifted lower.

As of 12:40 p.m. CDT (1740 GMT), Chicago Board of Trade December corn was up 1/2 cent at $3.26-3/4 per bushel, a day after dipping to a one-month low of $3.26.

Benchmark November soybeans were up 2 cents at $8.87-1/4 a bushel while CBOT September wheat was down 2 cents at $5.30-3/4 a bushel.

Corn futures hit a session high of $3.29-1/2 after the U.S. Department of Agriculture confirmed sales of 1.937 million tonnes of corn to China, the Asian country's largest single-day purchase of the U.S. feed grain.

But the market pared gains as traders returned their focus to favorable weather that has stoked expectations for a huge U.S. crop. The USDA, which is scheduled to release updated monthly crop production forecasts on Aug. 12, currently projects the average national corn yield at 178.5 bushels per acre, a record high if realized.

Analysts are considering the possibility of a yield above 180 bushels per acre.

"If I had to guess, we are going to see a noticeable hike in (corn) yield, and it will more than offset any demand decrease that the USDA puts out," said Tom Fritz, a partner at EFG Group in Chicago, referring to the USDA's Aug. 12 report.

Good weather in most of the Midwest also capped rallies in soybean futures, despite better-than-expected weekly export sales data. The USDA reported soybean export sales in the week ended July 23 at more than 3.6 million tonnes, above a range of trade expectations.

Traders are also expecting big crops in Brazil, where farmers will start planting soybeans in September. Brazil's soy 2020-21 harvest is expected to jump to top 130 million tonnes, according to a Reuters analyst poll. (Additional reporting by Nigel Hunt in London and Naveen Thukral in Singapore; Editing by Subhranshu Sahu, Devika Syamnath and Jonathan Oatis)