GRAINS-Soybeans sink on plentiful stocks, corn retreats

* Soybeans touch 3-week high, turn lower on big stocks

* Corn eases from 2-1/2-week peak after bullish acres

* Markets on edge after China tariffs on some imports

CHICAGO, April 2 (Reuters) - U.S. soybean futures were lower on Monday as early-session support from a lower-than-anticipated government forecast on spring plantings faded and investors turned their focus to plentiful U.S. supplies.

Corn futures notched a 2-1/2-week high on the U.S. Agriculture Department's bullish acreage forecast late last week, but gave back much of the day's gains as soybeans retreated.

The USDA on Thursday forecast U.S. plantings of both corn and soybeans below trade expectations, sending futures soaring ahead of the long Easter holiday weekend. The agency also estimated quarterly U.S. stocks of both commodities at historic highs, which the market largely shrugged off.

"After a three day weekend and a surprisingly bullish acreage number, the stocks number for soybeans is beginning to set in," said Ted Seifried, chief ag market strategist with Zaner Group.

"The market wants to be excited about the combination of Argentina (drought) and lower acreage, but we're still not in a position where the balance sheet gets tight," he said.

Chicago Board of Trade May soybeans fell 4-3/4 cents to $10.40 a bushel by 11:48 a.m. CDT (1648 GMT) after touching a three-week high of $10.60-1/2. A sharp drop in soymeal prices added pressure.

CBOT May corn was up 1/2 cent at $3.88-1/4 a bushel.

Fears of a trade war with China, a top agricultural products buyer, kept markets on edge after Beijing announced higher tariffs on a long list of U.S. goods, including pork and ethanol.

CBOT May soft red winter wheat declined 3-1/4 cents to $4.47-3/4 a bushel after hitting technical resistance at its 100-day moving average.

K.C. May hard red winter (HRW) wheat gained 1-3/4 cents to $4.69 a bushel amid forecasts for dry weather in the southwest U.S. Plains, where the crop has suffered under a severe drought.

The USDA is due to release updated crop condition ratings for wheat after the close on Monday. (Reporting by Karl Plume Editing by James Dalgleish)