WASHINGTON (AP) — The government will buy up to $170 million of pork, lamb, chicken and catfish to help drought-stricken farmers, the White House said Monday as President Barack Obama brought his re-election campaign to rural voters in Iowa.

The purchase for food banks and other federal food nutrition programs is expected to help producers struggling with the high cost of feed during the worst drought in a quarter-century.

Federal law allows the Agriculture Department to buy meat and poultry products to help farmers and ranchers affected by natural disasters.

The announcement came as Obama criticized Republican vice presidential candidate Paul Ryan for blocking a farm bill that could help farmers cope with the drought. Obama touted his efforts to help farmers as he began a three-day tour of the battleground state he won in 2008.

"The purchases will help mitigate further downward prices, stabilize market conditions and provide high quality, nutritious food to recipients of USDA nutrition programs," Agriculture Secretary Tom Vilsack said in a statement.

The USDA said it would buy up to $100 million of pork products, $50 million of chicken, $10 million of lamb and $10 million of catfish. The Defense Department, a large purchaser of beef, pork and lamb, was expected to look for ways to encourage its vendors to speed up purchases of meat.

Obama has pledged a wide-ranging response to the drought. His administration is giving farmers and ranchers access to low-interest emergency loans, opening more federal land for grazing and distributing $30 million to get water to livestock.

Many ranchers have sold off livestock as feed costs rise and their pastures dry up. The selloff is expected to lead to lower prices through December with a glut of meat on the market, but higher costs beginning next year.

Severe drought across the nation's midsection has sent corn prices soaring by nearly 23 percent. More than half of all U.S. counties have been designated primary disaster areas this growing season, mostly due to drought.