Washington ? The vending machine industry, taking heavy criticism as children and other Americans get fatter, is launching an anti-obesity marketing campaign to improve its image and fend off efforts to remove machines from schools.

A big part of the effort: color-coded stickers on vending machines to separate healthful items from those that hungry snackers should, in the industry’s words, “choose rarely.”

The National Automatic Merchandising Assn.’s effort, “Balanced for Life,” includes computer software available to schools for $100 that was developed by a hospital to rate food by color codes.

The move comes a day after the government issued guidelines urging Americans to exercise 30 to 90 minutes a day, eat less and choose whole grains, fruits and vegetables.

“People are going to eat what they want to eat,” said Richard M. Geerdes, the association’s president and chief executive. He said that when some schools in Los Angeles removed vending machines, consumption of snack food “shifted to a different source.”

“A solution like that doesn’t work,” Geerdes said.

The industry is promoting the “Snackwise Nutrition Rating System,” developed by Columbus Children’s Hospital in Columbus, Ohio.

The software evaluates the nutrition content of food based on calories, fat, sugar, protein, fiber, calcium, iron and vitamins A and C. A snack is assigned a point value, which is then translated into a color. Green is “best choice,” yellow is “choose occasionally” and red is “choose rarely.”