CHICAGO, Jan 12 (Reuters) - U.S. corn and soybean harvests in 2022 were smaller than previously estimated as crops struggled late in their development after a promising start to the growing season, the U.S. government said on Thursday.

Dry conditions also caused the U.S. Agriculture Department to cut its forecasts for corn and soybean production in key global supplier Argentina as the crops being grown there are wilting in a drought.

The reduction in the corn and soybean production estimates adds to worries about tightening global supplies of grains and resulting high food prices. U.S. corn production was at a three-year low and the soy crop was the smallest in two years.

"USDA made drastic cuts to the size of last years corn and soybean crops," said Joe Vaclavik, president of Standard Grain. "That's the big surprise today."

USDA does not normally make such sizeable cuts to crops that were harvested months ago.

The government also reported that U.S. farmers planted the largest winter wheat acreage in eight years, but analysts said the dry soils the crop was seeded in could crimp harvest yields.

Chicago Board of Trade soybean and corn futures surged to session highs after the data was released. K.C. hard red winter wheat futures also rallied.

U.S. corn production totaled 13.730 billion bushels in the 2022/23 marketing year, the U.S. Agriculture Department said in its monthly World Agricultural Supply and Demand Estimates report. That was down 200 million bushels from a month earlier and below a range of market expectations.

The production shortfall stemmed from a reduction in harvested acres, which fell to 79.2 million from the December forecast of 80.8 million as farmers opted not to bother harvesting damaged crops after a hot, dry August.

The U.S. soybean harvest came in at 4.276 billion bushels, down from the December estimate of 4.346 billion, with average yield per harvested acre dropping to 49.5 bushels from 50.2. USDA also lowered its harvested soybean acreage figure by 300,000 to 86.3 million.

In Argentina, USDA forecast a soybean crop of 45.5 million tonnes, 8.1% lower than its December outlook, and a corn crop of 52.0 million tonnes, down 5.5% from the December estimate.

U.S. winter wheat plantings totaled 36.950 million acres, a jump of 11% from the previous year and well above trade forecasts that ranged from 33.38 million to 36.20 million. (Additional reporting by Christopher Walljasper and Karl Plume; Editing by Alexander Smith)