WASHINGTON — Add schools to the list of places hit hard by rising food prices.

The school lunch program — long a reliable source of food for kids — is having serious trouble making cheap, healthful meals.

The culprit is food prices that have rocketed higher as fuel prices rise. It's not just the zooming cost of oil and gas. Food prices are also driven by demand for corn-based ethanol, worldwide demand for food and the weak dollar, among other things.

These far-flung factors have combined to put the squeeze on school kitchens, which provide free and reduced-price lunches, as well as full-price lunches, for more than half of the nation's 60 million schoolchildren.

"We are struggling to make ends meet," Katie Wilson, president-elect of the School Nutrition Association, told members of the House Education and Labor Committee on Wednesday. "We simply don't have the funds to continue on with this."

Next year, most schools plan to charge more for full-price meals, in addition to cutting staff, according to preliminary results of a School Nutrition Association study.

Schools can't put just anything on a child's lunch tray. Because the government subsidizes lunches, schools are expected to follow federal guidelines for healthy eating by providing lots of fresh fruit and vegetables, along with whole grains.

Those are the very foods hit hardest by the rising cost of food, as are milk and meat, two universal offerings in school lunch rooms.

It costs more to serve fruit and veggies, in part because they are processed less, if at all, which makes it harder to spread around the cost. And it costs more to serve milk and meat, because they come from farm animals that eat mostly corn.

Even a one-penny increase in the cost of milk can cost the nation's schools another $54 million, said Pavel N. Matustik, chief food services administrator of the Santa Clarita Valley School in California.

The government reimburses schools $2.57 for each meal, but for many districts, the cost of a lunch is well over $3, Wilson said.

The price of milk prompted Matustik to ask whether schools should even have to serve milk with every meal, a question he acknowledged would get him in trouble with the nation's dairy farmers.

Overall, food prices are expected to rise as much as 5.5 percent this year, with a slightly bigger increase for food that people make at home and a smaller increase for food in restaurants, the Agriculture Department said.

There is a dispute over how just much the booming ethanol industry is to blame for high food prices.

The department has said that close to 10 percent of the increase in food prices may be due to ethanol — because it increases demand, and therefore prices, for corn as well as the price of land for other commodities. But the food industry pointed out many other global estimates saying a much larger percentage is due to ethanol.

Regardless, those who testified agreed on one thing: Food prices aren't going back down. At the same time, more families will be turning to the school lunch program: The government expects an increase of about 1.5 percent.

"I think the price levels we're at now are not going to go down anytime soon," said Ephraim Liebtag, an Agriculture Department economist.