Agriculture Secretary Tom Vilsack is warning Americans to be on the lookout for food price gouging, as the historic drought creates an opening for stores to overcharge unsuspecting customers.

Echoing the views of other agriculture industry analysts, Vilsack said Wednesday that as the drought batters America's crop supply, prices at the checkout line could eventually rise as a result. But that won't happen yet, he said, suggesting that any shopkeepers who dramatically raise prices now are just trying to scam customers.

"The important thing right now is for consumers to be aware," Vilsack said.

Vilsack urged shoppers to scrutinize any "dramatic increase" in food prices they see. "If someone says, 'it's the drought,' they should push back," Vilsack said.

Vilsack said customers should not see food price increases at grocery stores until later this year, or early next year. The secretary said ranchers' herds are also suffering from the drought, and that the price of beef, poultry and beef could likewise rise later this year, or early next year.

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The Obama administration meanwhile called on Congress to provide assistance to farmers suffering from the worst drought in 25 years. Vilsack said three-fifths of the U.S. land mass and much of the country's corn and soybean crops are affected by the lack of rain.

Vilsack spoke at the White House press briefing Wednesday after meeting with President Obama to discuss a response. Vilsack said farmers could get assistance if Congress passes a new farm bill, approves additional disaster programs or provides more flexibility in the availability of credit.

He said the president has also given the go-ahead for lower interest rates on loans to affected farmers, and for new areas to be opened up for emergency grazing -- in response to the high cost of livestock feed.

In its monthly drought report, the National Climatic Data Center in Asheville, N.C., announced that 55 percent of the country was in a moderate to extreme drought at the end of June. The parched conditions expanded last month in the West, the Great Plains and the Midwest, fueled by the 14th warmest and 10th driest June on record, the report said.

Topsoil has turned dry, while "crops, pastures and rangeland have deteriorated at a rate rarely seen in the last 18 years," the report said.

The Associated Press contributed to this report.