COUNCIL BLUFFS, Iowa—President Barack Obama offered aid to the agriculture industry and took aim at his new rival on the Republican presidential ticket, Rep. Paul Ryan, at the start of a three-day campaign swing through the battleground state of Iowa on Monday.

Flexing the power of incumbency, Mr. Obama used his first stop in Iowa to announce that the Agriculture Department would purchase $170 million of pork, chicken, lamb and catfish in an attempt to alleviate the burden put on U.S. farmers from the drought. The purchases will be used in food-aid programs, the White House said.

Underscoring the importance of Iowa in the November election, Mr. Ryan was also in the state Monday for his first solo campaign appearance since Republican presidential candidate Mitt Romney tapped him as his running mate on Saturday.

In his own appearance, Mr. Obama singled out Mr. Ryan, whom he described as the GOP's "ideological leader," as he accused congressional Republicans of blocking federal aid for farmers and ranchers as part of stalled farm legislation.

"I am told Gov. Romney's new running mate, Paul Ryan, might be around Iowa these next few days," Mr. Obama told a crowd of supporters.