* U.S. soy, corn harvest under way amid favorable weather

* Soymeal buoyed as Argentine crush pace lags

* Corn ends fractionally lower on U.S. harvest pressure

* Egypt buys Russian wheat at international tender

* Corn capped by surprise crop ratings improvement

CHICAGO, Sept 22 (Reuters) - Chicago soybean futures ended lower on Tuesday, retreating from early strength as pressure from the expanding U.S. harvest outweighed support from continued soy sales to China and strength in soymeal futures, traders said.

Corn futures drifted lower on strong U.S. crop ratings and promising Midwest harvest weather, but wheat gained on international export demand.

The most-active soybean contract on the Chicago Board of Trade (CBOT) ended 2-3/4 cents lower at $10.19-3/4 per bushel.

CBOT wheat ended up 3-1/4 cents at $5.58 a bushel, while corn finished down 1/2 cent at $3.69-1/4 a bushel.

"You're at a technical selling point on soybeans, as well as seeing harvest pressure," said Dax Wedemeyer, broker/analyst at Iowa-based U.S. Commodities. "We’re hearing better-than-expected yield reports. That’s cooled the rally a bit."

The USDA said late on Monday that U.S. farmers had completed 6% of the soybean harvest and that the corn harvest was 8% complete. Forecasts called for fair Midwest weather over the next two weeks that should keep combines rolling.

On the demand side, the USDA confirmed sales of 266,000 tonnes of U.S. soybeans to China and 264,000 tonnes to unknown destinations, marking the 13th consecutive business day of sales to China. The USDA also reported sales of U.S. corn to China and unknown destinations.

A reduced soybean crush in Argentina, the world's top supplier of soymeal and soyoil, lifted U.S. soymeal prices, said Terry Reilly, senior analyst with Futures International. The front four CBOT soymeal futures contracts set life-of-contract highs on Tuesday.

Wheat futures advanced, supported by robust global export business.

"Cash (wheat) prices in the Black Sea region are up four weeks in a row," said Reilly.

Egypt's state wheat buyer, the General Authority for Supply Commodities (GASC), purchased 405,000 tonnes of Russian wheat at around $256 per tonne (including freight), up about $7 a tonne from what it paid in a similar tender last week. (Reporting by Christopher Walljasper; Additional reporting by Gus Trompiz in Paris and Naveen Thukral in Singapore; Editing by Richard Chang and Peter Cooney)