The Agriculture Department wants to change the content of federally subsidized school meals — 33 million lunches and 9 million breakfasts a day — by the fall of 2012. Beyond the calorie cap, the new standards would emphasize whole grains, vegetables and fruits and set tighter limits on sodium and fats.

“This will mean a huge shift in school meals,” said Margo G. Wootan, the director of nutrition policy at the Center for Science in the Public Interest, a consumer advocacy group.

Fernando Gallard, a spokesman for the Philadelphia School District, said schools were meeting the new federal meal proposals by using more dark green and orange vegetables, as well as fruits, whole grains and legumes.

The food industry is defending products by focusing on their mineral and vitamin content. The National Potato Council, for example, is warning against cutting starch, saying children need potatoes’ potassium and fiber.

Some companies are adjusting their recipes, although hardly drastically. After Philadelphia schools stopped buying the sugary products of the local bakery icon Tastykake, the company created a 190-calorie muffin, reducing sugar enough to move it below flour on the list of ingredients. The new formulation, which uses whole grains, got Tastykake muffins back on the school breakfast menu and classified as bread. “It is sweet,” said Autumn R. Bayles, a company senior vice president. “Sugar is just not the first ingredient.”

To match the efforts inside the school, one of Ms. Brown’s first acts as principal last August was to ask owners of nearby corner stores to stop selling to students in the morning.