By Tom Polansek

CHICAGO (Reuters) - A storm packing hurricane-force winds on Monday impacted 37.7 million acres of farmland across the Midwest, including 14 million in Iowa, the Iowa Soybean Association said on Friday, citing estimates from the U.S. Department of Agriculture.

The toll from the derecho storm has worsened as farmers and grain handlers have spent the week assessing flattened corn fields and crumpled steel storage bins.

The USDA said the storm affected 8.18 million acres of corn and 5.64 million acres of soybeans in Iowa, according to the Iowa Soybean Association. The state agriculture department on Tuesday estimated a total of 10 million acres may have been impacted.

The storm affected 58,000 holders of crop-insurance policies with a liability of around $6 billion in Iowa, including $1.86 billion for soybeans, the Iowa Soybean Association said, citing data from the USDA's Risk Management Agency.

The Risk Management Agency released the estimates to farm and commodity groups on Friday, Iowa Soybean Association spokesman Aaron Putze told Reuters. He said the information was intended to encourage farmers to assess their losses and file claims for crop insurance.

"We knew it was big, but it's bigger than we even anticipated it would be in terms of the acres it affected," Putze said.

Risk Management Agency representatives could not immediately be reached for comment.

The agency has urged farmers to expedite the filing of loss claims, according to Iowa Soybean Association. Claims are supposed to be filed within 72 hours of identifying losses, but allowances will be made for those suffering from disruptions in telephone and communications services, the farm group said.

"USDA is standing by to help impacted producers and strongly encourage farmers and livestock producers who experienced losses or damage to contact their local USDA Service Center," said Dirk Fillpot, a USDA spokesman.