(Updates with closing prices)
CHICAGO, Sept 7 (Reuters) - U.S. corn futures on Thursday sagged 1.7 percent on technical selling and expectations of a U.S. bumper harvest that would enlarge the already massive global supply of the grain, traders said.
Wheat and soybean futures also posted lower closes. Wheat faced pressure from weak worldwide demand for U.S. supplies and a round of profit taking following a run-up to the three-week high hit on Wednesday.
Soybeans ended in negative territory after trading higher for much of the day. Corn's drop to session lows spilled over to soybean futures late in the session. The soybean market's failure to hold support above Wednesday's high also added to the bearish tone.
But concerns that Hurricane Irma will cut production in southern states such as Georgia and North Carolina limited the sell-off in the soy complex.
"The beans are being supported by the hurricane," said Mark Gold, managing partner at Top Third Ag Marketing. "It is going to do some damage there."
Chicago Board of Trade December corn futures ended down 5-3/4 cents at $3.55-1/4 a bushel, settling near session lows.
Corn futures firmed during overnight trading but hit resistance at their 20-day moving average, a level the December contract has not broken through since Aug. 10. Corn prices also tested that key technical point on Wednesday.
Traders also noted profit-taking following the corn market's run-up to a two-week high on Wednesday.
CBOT December wheat futures dropped 8-1/2 cents to $4.37-1/4 a bushel.
Irma, which is expected to hit the U.S. mainland as early as this weekend, could also hamper exports, which would be another blow to the already light overseas interest in U.S. wheat stocks.
"Traders are also monitoring the Irma hurricane as its trajectory could hit the U.S. south-eastern coast, surely causing logistical issues," French consultancy Agritel said.
CBOT wheat had risen for four straight sessions and five of the previous six. Traders said that had caused some funds to back out of bullish bets built up during that run.
CBOT November soybeans were down 2-1/4 cents at $9.68-3/4 a bushel. (Reporting by Mark Weinraub in Chicago; Additional reporting by Naveen Thukral in Singapore and Sybille de La Hamaide in Paris; Editing by W Simon and Grant McCool)