HARRISBURG — A proposal in Pennsylvania that backers say would be the most comprehensive in the nation to motivate public schools to combat childhood obesity got a preliminary stamp of approval Thursday.

The Pennsylvania State Board of Education voted to advance a draft regulation that would greatly increase the exercise that most students currently get during school hours and toughen nutritional guidelines for the food served in public schools.

The measure, which applies to students in kindergarten through 12th grade, was approved 15-1. It now must be posted in the Pennsylvania Bulletin so that the public can submit comments on it and it faces what could be a months-long public review by the House and Senate Education committees before a state regulatory board can vote on it.

Changes are likely, especially considering that even many education groups that support the proposal's overall goals also worry about costs and providing children with enough academic time to meet state and federal testing benchmarks.

The state secretary of health, Everette James, appeared before the board with three middle school principals to argue for the proposal.

"This is a historic step being taken today," James said in an interview outside the meeting. With respect to concerns about expenses and fitting in the activity time, he said, "It can be done if it's a priority."

The state spends $1.5 billion to $2 billion a year in taxpayer money to treat the obesity-related health problems of people enrolled in the state's Medicaid program. Meanwhile, one-third of all Pennsylvania students are overweight or obese, with higher rates than that in 43 of 67 counties, James said.

The measure would likely banish many of the processed foods served in schools because of the guidelines that it would set for fat, sugar, sodium and calories.

In addition, it would require school districts to provide physical education classes and a minimum of 30 minutes of daily exercise; the state does not currently set any minimum physical activity requirements. Students in after-school sports would not be excused.

The three principals who appeared with James said students, as well as teachers, have embraced similar steps they've taken in their schools. The Riverside Beaver County district created a 16-station wellness center with money from grants and community donations after administrators discovered that 50 percent of students were obese. Before students took state assessment tests last year, they were encouraged to use the center.

"Our scores actually rose dramatically last year," said Steve Girting, the district's middle school and intermediate principal.

Jim Buckheit, the executive director of the Pennsylvania Association of School Administrators, said the trend in schools has been to cut back on things like recreation and physical education in order to reserve more time for subjects on which students are tested.

Also, he said some accommodation must be made for students in after-school sports.

Elizabeth Walker, who directs a healthy schools project for the National Association of State Boards of Education, said Pennsylvania's proposal, if approved, would put it at the forefront of state efforts.

A number of states have obesity-prevention policies, but many only encourage districts to take steps, while others do not extend the requirements to high schools, she said.