Each color scores the product on its nutritional worth.

Richard Geerdes, president of the Washington trade group representing the $30 billion industry, said vending-machine operators would work primarily with school systems to set up the program this year.

About 16.3% of the nation's 7 million vending machines are found in school campuses and colleges, Geerdes said.

The trade association has invested about $1.5 million in the campaign so far.

Some 15% of American children are overweight or obese, according to the Centers for Disease Control and Prevention.

"We know that there is a problem with childhood obesity in this country, and we want to be part of the solution instead of unfairly being labeled as part of the problem," Geerdes said, referring to numerous school boards nationwide that have cut back on or banned school vending machines.

The snacks were scored on a point basis. The system gives a point to foods rich in calcium, protein, fiber, iron and vitamins A and E while taking away points from those high in sugars, fats and calories.

A poster explaining the ratings will be placed on the outside of each machine.

At the vending-machine-association press conference, green stickers were placed on items such as pretzels, Nutri-Grain cereal bars and Go-Gurt yogurt, advising consumers to frequently choose those items.

Other products like Wheat Thins, Starburst Fruit Chews and SnackWell's cookies were labeled yellow, suggesting to choose occasionally.

Austin crackers, Snickers, chocolate chip cookies and Doritos chips were labeled red, which advises to eat those products rarely.

The campaign comes amid a growing movement by food companies to offer healthier alternatives to their fatty products. Oreo cookie maker Kraft Foods Inc. recently announced that the company will focus its children's advertising on healthier fare and highlight nutritional information on its packaging.

The Center for Science in the Public Interest, a Washington health advocacy group that has pressured lawmakers and school boards to ban vending machines in schools, called the campaign a "public-relations ploy."

The center's executive director, Michael F. Jacobson, called for Lynn Swann, who appeared at the press conference to promote physical activity in schools, to be fired as chairman of the President's Council on Physical Fitness and Sports.

Swann, an NFL Hall of Famer who played wide receiver for the Pittsburgh Steelers, said he attended as a private citizen, adding "it is not a conflict of interest."

While the campaign does not insulate the vending-machine operators from class-action obesity lawsuits, it does put the industry in a better standing with the court, said Louise Ellingsworth, a class-action defense lawyer.

"Certainly in the environment we are in now, proactive steps by an industry appear to be very appreciated," said Ellingsworth, a partner at the Kansas City, Mo., office of international law firm Bryan Cave LLP.

The vending industry's message, of snacking moderately and exercising daily, mirrored the government's dietary guidelines released earlier in the week.

The campaign will closely monitor sales to determine its success, Geerdes said.

The program is only geared toward snack machines, but Geerdes said the campaign plans to develop a similar program for beverage machines. The American Beverage Association, a Washington trade group for the nonalcoholic beverage industry, said it had no immediate plans to join the campaign.

Local vending-machine operators said it was too soon to know if many schools will participate in the campaign.

"We just announced this, but we're hoping schools will get on board," said Craig Kushner, president of Monumental Vending. However, Dominic Finelli, an owner of Custom Vending Co., said he was skeptical the program would change children's eating habits.

"We put a warning label on cigarettes; some folks followed the label, and some didn't. I think it could work the same way with snacks. Ultimately, it's up to the school or company as to what they sell," Finelli said.