The Obama administration warned on Wednesday that crops were being spoiled and food prices might rise because of the worsening drought afflicting more than half of the country, and it called on Congress to revive lapsed disaster aid programs.

President Obama reviewed the situation with Tom Vilsack, the agriculture secretary, who called it “the most serious situation” in about 25 years, and added that he was praying for rain.

“I get on my knees every day and I’m saying an extra prayer now,” Mr. Vilsack told reporters at the White House after his discussions with Mr. Obama. “If I had a rain prayer or rain dance I could do, I would do it.”

Mr. Vilsack said 1,297 counties, or roughly a third of the counties in the nation, have been designated disaster areas. He said 39 more counties were being added on Wednesday.

More than three-quarters of the nation’s corn and soybean crops are in drought-affected areas and more than a third of those crops are now rated poor to very poor, Mr. Vilsack said. The price of corn has already increased in recent weeks by 38 percent and the price of beans is up 24 percent. The country may still have the third-largest corn crop in history because good weather earlier in the year encouraged planting, but Mr. Vilsack said the drought would result in price increases for food into 2013.

The cost of beef, poultry and pork may actually go down in the short term because those herds are being liquidated, putting more on the market, he said. But meat prices will probably rise later in the year or early next year.

He declined to speculate about whether the drought could be tied to climate change. “All we know is that right now there are a lot of farmers and ranchers who are struggling,” Mr. Vilsack said. “Rather than trying to focus on what’s causing this, what we can do to help them” should be the priority, he said.

The administration has already lowered the interest rate for emergency loans and has worked to streamline assistance programs. Mr. Vilsack said Congress could help by restoring disaster programs that expired last year or by providing other assistance through the Food, Farm and Jobs Act, a major overhaul of the nation’s nutrition and agriculture program now pending.