WASHINGTON — The U.S. Department of Agriculture today unveiled new nutrition standards for school meals, the first major changes in more than 15 years. The changes, which are expected to cost $3.2 billion over the next five years, include sharp reductions in sodium content in meals, minimum and maximum calorie levels, larger portions of fruits and vegetables, and more whole grains.

The changes are designed to improve the health of nearly 32 million children who eat lunch at school every day and almost 11 million who eat breakfast. The meal requirements are a key component of the Healthy, Hunger-Free Kids Act that was introduced in 2010.

“Improving the quality of the school meals is a critical step in building a healthy future for our kids,” said Secretary of Agriculture Tom Vilsack. “When it comes to our children, we must do everything possible to provide them the nutrition they need to be healthy, active and ready to face the future — today we take an important step towards that goal.”

The new standards for school lunch include:

•Establishing maximum calorie and sodium limits for meals. The sodium limits will be phased in over 10 years.

“To meet the final sodium target, schools will have to reduce the sodium content of the meals by approximately 25% to 50% from the school baseline,” the U.S.D.A. said. “This will require innovation on the part of product manufacturers in the form of new technology and/or food products.”

The U.S.D.A. noted that schools, by meeting the final sodium targets, will be able to offer meals that reflect the 2010 Dietary Guidelines’ recommendation to limit sodium intake to less than 2,300 mg per day.

•Requiring schools to serve a fruit and vegetable every day at lunch and in larger portions than offered before. Schools will be required to offer 1 cup of fruit to all age/grade groups at breakfast beginning in the 2014-15 school year.

•Requiring schools to offer a minimum number of dark green, red/orange, legumes, and starchy vegetables each week. The amount varies by age group. Additionally, the rule will allow schools the option to offer vegetables in place of all or part of the fruits requirement at breakfast beginning July 1, 2014.

“This recommendation is applicable to the school meals because most vegetables and fruits are major contributors of nutrients that are under-consumed in the United States, including potassium and dietary fiber,” the U.S.D.A. said. “Consumption of vegetables and fruits is also associated with reduced risk of many chronic diseases, including obesity, heart attack, stroke and cancer. By providing more and a variety of vegetables in a nutrient-dense form (without added solid fats, sugars, refined starches, and sodium), schools help students obtain important nutrients and maintain a healthy weight.”

•Requiring that after the two years of implementation, all grains offered to students must contain at least 51% whole grains with the remaining grain content enriched. Until the whole grain content of food products is required on a product label by the Food and Drug Administration, schools must evaluate a grain product according to forthcoming Food and Nutrition Service guidance. The guidance states that the serving of the food item must meet portion size requirements for the grains/bread component outlined by the F.N.S. and at least one of the following: (a) the whole grain per serving must be equal to or greater than 8 grams; (b) the product includes the following F.D.A.-approved whole grain health claim on its packaging, “Diets rich in whole grain foods and other plant foods and low in total fat, saturated fat and cholesterol may reduce the risk of heart disease and some cancers.”; or (c) product ingredient listing lists whole grain first, specifically non-mixed dishes like bread or cereal and mixed dishes such as pizza or corn dogs.

•Requiring milk to be either low-fat (1%) or fat-free. Flavored milk, such as chocolate, now must be fat-free.

“Flavored low-fat (1% or ½%) milk is not allowed in the N.S.L.P. or the S.B.P. upon implementation of the rule in SY 2012-13 because it contributes added sugars and fat to the meal and would make it more difficult for schools to offer meals that meet the limits on calories and saturated fat,” the U.S.D.A. said.

•Requiring that foods that are served contain no trans fats. The U.S.D.A. said the requirement is intended to restrict synthetic trans fatty acids and does not apply to naturally occurring trans fats, which are present in meat and dairy products. Synthetic trans fatty acids are found in partially hydrogenated oils used in some margarines, snack foods and prepared desserts.

The new standards for lunch take effect the next school year, 2012-13. Changes for breakfast will be phased in.

The U.S.D.A. estimated food costs initially will increase by 2.5c per lunch served, and two years after implementation. The U.S.D.A. also estimated that when the fruit requirement is phased in for breakfast and when all grains served at breakfast and lunch must be whole grains, the costs will increase by 5c per lunch and 14c per breakfast.

The U.S.D.A. received 132,000 public comments on the proposed standards.

“We know that robust public input is essential to developing successful standards and the final standards took a number of suggestions from stakeholders, school food service professions and parents to make important operational changes while maintaining nutritional integrity,” said Kevin Concannon, Undersecretary for Food, Nutrition and Consumer Services.