(New throughout, updates with U.S. trading, adds new analyst quote, changes byline, dateline; pvs PARIS/SINGAPORE)

CHICAGO, Aug 7 (Reuters) - U.S. soybean futures fell for the fourth day in a row to their lowest since June 30 as expectations kept building that growing supplies will outstrip demand even as top buyer China steps up its purchases, traders said.

A bearish supply outlook also pressured wheat futures, which dropped 1.8% to a one-month low, and the corn market.

Traders were staking out positions ahead of the U.S. Agriculture Department's monthly supply and demand report next week that analysts were expecting would boost the government's view of the supply situation for all three commodities.

"We have good growing conditions," president of broker Midwest Market Solutions. "We have a report that is next week that is expected to be a little bit bearish. Political tensions continue to rise. All those factors are bearish enough to continue to push this market lower.

At 10:52 a.m. CDT (1552 GMT), Chicago Board of Trade November soybean futures were down 9-1/4 cents at $8.68-3/4 a bushel.

USDA on Friday reported private sales of U.S. soybeans to China of 456,000 tonnes, the biggest single-day soy sale to the world's top buyer since June 11.

CBOT September soft red winter wheat 8-3/4 cents lower at $4.92-1/2 a bushel. The contract was on track for a weekly loss of 7.3%, which would be the biggest for the most-active wheat futures contract in nearly two years.

An estimate calling for a record Canadian wheat crop, rising forecasts for Russia's harvest, improving conditions in Australia and good early signs for the U.S. spring wheat harvest were underscoring ample global supplies.

"You've got four major countries in which wheat crop forecasts are being upgraded," said Nathan Cordier of consultancy Agritel.

CBOT December corn futures were off 3 cents at $3.20-3/4 a bushel. (Additional reporting by Gus Trompiz in Paris and Naveen Thukral in Singapore, Editing by Sherry Jacob-Phillips and David Gregorio)