Healthier snacks and fruit juices would replace junk food and sodas in vending machines at seven public schools in October, and throughout the District school system by February, under a resolution that the D.C. Board of Education unanimously approved last night.

The resolution adds the District to a growing list of cities that have moved to introduce healthier eating options at schools, prompted by concerns about an increase in childhood obesity. In the past few years, school boards in Los Angeles, Philadelphia and New York City have taken steps to improve the nutritional content of items sold in vending machines.

The Montgomery County school board voted in the spring to curtail the size of beverages and set limits on the saturated fat and sugar content of snacks. Virginia's legislature is considering a proposal to set nutritional standards for all food served inside schools, including food from vending machines.

The D.C. resolution states that "most vending machine snacks have little nutritional value, and are in direct competition with a healthy school lunch program," and cites research showing that healthier eating can improve students' concentration and behavior.

"If we want our children to be mentally ready to learn, then we must provide them with healthier choices to help them develop the physical and emotional muscle they need to be successful," said school board President Peggy Cooper Cafritz in a statement. "A healthy diet is fundamental to that."

The resolution is to take effect in October at Ballou, Cardozo, Roosevelt and Wilson senior high schools; Browne and Jefferson junior high schools; and Kramer Middle School. The resolution calls for the expansion of the effort to all public schools by February "based on the success of the pilot program" but does not say how success is to be assessed.

The resolution restricts the sale of beverages at the seven schools to water, low- and fat-free milk and drinks that contain at least 50 percent fruit juice. It sets limits of 7 grams of fat and 15 grams of sugar for snacks sold in vending machines, with exceptions for nut and seed mixes and dried fruits. It also establishes maximum portion sizes for chips, cookies, beverages, yogurts, pastries and frozen desserts, including ice cream. The resolution calls for implementing a marketing campaign by January to teach students about the importance of healthy eating.

Interim Superintendent Robert C. Rice said he supported the measure. "The time is right for us to begin this process of installing nutritious foods in school vending machines," Rice said through his chief of staff.

Nutritionists and representatives of research and advocacy groups, who have pushed for the change in the District over the past year, testified in support of the resolution last night.

Kimberly Perry of the Food Research and Action Center, a policy group based in the District, chaired a group of parents, educators and health professionals that conducted focus groups at several of the seven schools in the pilot program.

"The call for healthier snacks and beverages was one we heard loud and clear," Perry said. "Students told us they wanted more choices and that they'd like to participate in the decisions being made about beverages and snacks that go into their school's vending machines."

Perry also argued that unhealthy snacks are self-defeating. "The availability of junk food in schools undercuts participation in national school meal programs and undermines health and nutrition education provided to students," she said.

Joy M. Johanson, a researcher at the District-based Center for Science in the Public Interest, said that a sharp rise in children's caloric intake since the late 1970s has contributed to rising rates of obesity, diabetes and elevated cholesterol and blood pressure.

There are many reasons why children buy food from machines at school, Johanson said, citing long cafeteria lines, short lunch periods and extracurricular activities during the lunch period that reduce the amount of time children spend eating.

"Schools should practice what they teach," Johanson said. "Selling low-nutrition foods in schools contradicts nutrition education and sends children the message that good nutrition is unimportant."

However, Reuben L. Gist, of the Capital Area Food Bank, questioned whether the resolution would affect children's eating habits.

"They will spend their limited disposable finances at the local mom-and-pop stores on the junk food they once purchased from the vending machines," he said. Gist argued that the focus should be on enrolling all eligible children in federally funded school food programs and on nutrition education.

The Government Accountability Office, at the request of members of Congress, is examining the prevalence and impact of vending machines in public schools across the United States, according to Barry D. Sackin of the American School Food Service Association, which represents school nutritionists.

In an interview, Sackin took care not to fault operators of vending machines. "It's not vending machines that are the problem, but what's in vending machines," he said. Sackin added that several school districts have successfully sold enough low-fat chips, pretzels, water and milk to make up for the loss of revenue from less-healthy snacks: "You can make substitutions in your vending program and still show a profit, a good profit, without the negative nutrition impacts," he said.