GRAINS-Soy falls to 4-month lows ahead of USDA data; corn, wheat flat

* Traders await USDA data due at 11 a.m. CST (1700 GMT)

* China soybean imports hit second-highest on record in Dec (New throughout, updates prices, market activity and comments; new byline, changes dateline, previously LONDON)

CHICAGO, Jan 12 (Reuters) - U.S. soybean futures dropped to four-month lows on Friday, on pace for the fourth consecutive session of declines ahead of U.S. government crop data due at midday that was expected to show bigger global soy supplies.

Chicago Board of Trade March soybean futures skidded to a session low of $9.45-1/2 per bushel, down 4-1/2 cents, by 10:20 a.m. CST (1620 GMT), ahead of the data due at 11 a.m. CST.

CBOT March wheat up 1-3/4 cent to $4.35 per bushel and CBOT March corn was unchanged at $3.48-3/4.

The U.S. Department of Agriculture, in one of its largest data releases of the year, was likely to forecast smaller U.S. soybean exports, larger Brazilian soybean production, and decreased U.S. winter wheat plantings.

"USDA is expected to lower U.S. (soy) exports and raise stocks in this week's report, due to the ongoing slowness of exports. This, combined with large global supplies, continues to pressure markets," David Sheppard, managing director of UK merchant Gleadell said in a market note.

Dealers said trading activity was subdued ahead of the data, which may reinforce concerns about excess grain and soy supplies.

Grain prices were underpinned by a weaker dollar, which eased to a four-month low against a basket of currencies, making U.S. goods comparatively less expensive in global markets.

Additionally, USDA in its daily export sales reporting system announced a sale of 320,000 tonnes of U.S. corn to unknown destinations - the largest one-day sale of corn since November.

Soy prices remained anchored by good crop conditions in Brazil, which could reap a record-large soy harvest in the coming months.

"Brazilian crop is looking good. There is dryness in Argentina but that will not make a huge difference as there are plenty of supplies," said Phin Ziebell, agribusiness economist at National Australia Bank.

"Chinese demand is pretty strong, the December imports are big but right now the market is influenced by production, so it a supply side of story."

Chinese imports of soybeans jumped to the second-highest volume on record in December, according to Reuters calculations based on customs data, boosted by strong demand in the run-up to next month's Lunar New Year holiday. (Additional reporting by Nigel Hunt in London and Naveen Thukral in Singapore; Editing by David Gregorio)