Soybean futures stumble as traders await US crop data

* U.S. to issue monthly supply/demand data on Sept. 12

* Analysts expect cuts to U.S. corn, soy output

* U.S. corn harvesting starts early in some areas

CHICAGO, Sept 7 (Reuters) - U.S. soybean futures fell on Thursday as the market consolidated and traders waited for updated crop estimates due next week.

Corn futures were nearly unchanged amid uncertainty over early U.S. harvest results.

The U.S. Department of Agriculture is slated to issue monthly crop data on Sept. 12, giving traders the latest outlook for global production after recent heat and dryness lowered U.S. crop condition ratings.

Analysts on average expect the USDA to trim U.S. production and yield estimates from August in the World Agricultural Supply and Demand Estimates (WASDE) report.

"I think you're in a hurry up and wait, consolidation mode," said Jim Gerlach, a market analyst and president of A/C Trading. "I doubt you're going to move either side of that at least until we get that September crop report or we move deeper into harvest."

Most-active soybean futures were down 14-1/2 cents to $13.61-3/4 a bushel by 11 a.m. CDT (1600 GMT) at the Chicago Board of Trade. Wheat futures eased 4-1/4 cents to $6.04-3/4 a bushel, while corn was down half a cent at $4.85-1/4 a bushel after touching a one-week high on Wednesday.

"Corn was sideways overnight," brokerage CHS Hedging said. "We may just glide into next week's WASDE report."

Corn harvesting in parts of the western U.S. Midwest is starting sooner than normal following the hot, dry weather. The crop's rapid finish may threaten grain quality or yields.

"Harvest is coming on fast, which should be a warning," Gerlach said. "When your crop dies down instead of dries down, it costs you some yield."

In Brazil, farmers should produce a record 131.8 million metric tons of corn, Brazilian food supply agency Conab said on Wednesday.

Grain traders also monitored tensions in the Black Sea region. Russia carried out its fourth drone attack in five days on Ukrainian port facilities on the Danube River, damaging grain silos on a vital export route for Kyiv, Ukraine said. (Reporting by Tom Polansek in Chicago; Additional reporting by Gus Trompiz in Paris and Naveen Thukral in Singapore; Editing by Rashmi Aich, Emelia Sithole-Matarise and Paul Simao)