They’re not quite the scary androids of “I, Robot,’’ but snack and soda vending machines in many schools are nearly as controversial. They’re seen as villains by nutritionists fighting childhood obesity, as saviors by principals seeking extra cash from access fees to pay for band uniforms, class trips and senior proms.

But, with childhood obesity in the news regularly, the two sides are getting more vocal, with advocates for healthier student snacks and lunches on one side and lucrative contracts from fast-food outlets and vending machine companies on the other.

In the Miami-Dade district, the 170 snack vending machines in public high schools and vocational schools for the first time must have half their slots filled with “healthy’’ snacks. (The rest can be the salty, deep-fried chips.)

The 413 beverage vending machines have to be divided accordingly: One-third low-fat milk (1 percent), one-third water, 100 percent fruit juice or approved sports drinks and one-third soda, with one slot dedicated to 100 percent fruit juice in the soda machines.

But there’s a catch: Instead of opening only a few hours during the school day, the vending machines can stay open all day. Penny Parham, administrative director of Miami-Dade Schools’ Department of Food and Nutrition, said the healthier snacks make the limited hours unnecessary.

One soda and juice vendor predicted a 30 percent jump in sales.

Money is a big reason for the vending expansion proposals, says Lilia Garcia, head of Miami-Dade’s Division of Life Skills and co-chair of the committee that made the recommendation. This year eight snack and beverage vendors will pay more than $2.7 million for exclusive hallway access for their machines in Miami-Dade’s 37 high schools and vocational schools, a $400,000 increase over last year.

“Those schools are asking for some of that revenue,’’ said Garcia. “They’d like a little of the action.’’

The new vending rules are part of a systemwide overhaul of school nutrition done over the past six months by a Dade Food and Nutrition Advisory Committee (FNAC) appointed last October by Dr. Michael Krop, chairman of the Miami-Dade School Board.

Nutritionists have hailed many of the changes, under which Miami-Dade schools will:

_Offer free breakfasts to all students.

_Cut high-fructose corn syrup, saturated and trans fats in cafeteria lunches.

_Offer 100 percent fruit juice in the soda machines.

_Require snack vending machines to set aside half their slots for “healthy’’ snacks that get 35 percent or less of their calories from fat, contain no more than 10 percent saturated fat and no more than a half gram of trans fat, and have 240 milligrams or fewer of sodium.

But the new rules will continue to allow lunchtime hallway kiosks in high schools to sell Domino’s and Papa John’s pizzas, Subway subs and McDonald’s Quarter Pounders with Cheese, hamburgers and cheeseburgers. These offerings are not subject to the USDA nutrition rules that govern cafeteria food. Rather, they’re a product of overcrowded cafeterias: American Senior High, for example, has a 300-seat cafeteria and nearly 2,900 students.

Here, Parham has won modest reforms: “We’re trying a new pizza that we make, with controlled fat and sodium.’’ But the Quarter Pounders will remain, she says.

“We did the best we could,’’ said Parham, who was on Garcia’s committee. “Fifty percent healthy snacks is a doable transition.’’

Still, the vending machine compromise fails to meet recommendations made earlier this year by both the Dade Food and Nutrition Advisory Committee and the Governor’s Task Force on the Obesity Epidemic. Both had urged schools to make sure that all food and beverages on school campuses, including vended food, meet the same USDA dietary guidelines as cafeteria lunches.

For years, Dade high school principals have permitted vending machines in their hallways in return for access fees that pay for class trips, senior proms, band uniforms and other expenses not fully funded by the school system.

On July 14, the Miami-Dade School Board accepted $2,753,892 in bids from eight firms for the right to vend soft drinks, milk, snacks and ice cream to 109,594 students in Miami-Dade’s 37 high schools and vocational schools this year. At its Aug. 18 meeting, the School Board revised the bids slightly, netting $2,748,892 to the schools.

Under this year’s contract, American Senior High School in Hialeah, Fla., for example, will receive $87,342 in vending machine fees, made up of:

_$42,700 from Gilly Vending of North Miami Beach for milk and snack vending machines;

_$41,342 from Coca-Cola Enterprises for soda, water, juice and sports drink machines;

_$3,300 from MICI Vending of Hialeah for ice cream vending machines.

Applied to American’s attendance of 2,854 last year, the companies are paying $30.60 a student for the exclusive access.

American High Principal Louis Algaze says he spends the money on extra textbooks for advanced placement courses – which can run as high as $70 each – and bus trips to local colleges.

“High schoolers are going to buy what they want anyway, here or across the street at the gas station after school.’’

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NEW RULES MAY TAKE BITE OUT OF SALES

You think it’s easy running vending machines in high schools? Just ask Gilda Rosenberg, president of Gilly Vending of North Miami Beach, who’s paying $1,260,800 this year for exclusive access for her snacks and beverages in Miami-Dade Schools’ 37 high and vocational schools.

“I lost money last year. It’s the donations you have to make, the tech support you need. Thirty percent of my profit went to vandalism. Pretty soon nobody will bid.’’

It hasn’t happened yet. School officials say this year’s $2.7 million in access fees from eight Florida vending companies is up from $2.3 million last year.

Rosenberg says she’ll lose even more this year under Dade’s new rules, which require vending machines to fill half their slots with “healthy’’ snacks lower in salt and fat. She’ll try, with low-fat Cheetos, 1 percent milk, 100 percent juices. She doubts it will work.

“You go healthy, profits go down by 30 percent,’’ she said. “Vending is for a specific kind of craving. It’s not for the apple you might eat in your house in the morning. From a vending machine you want something crunchy, energetic, something you like.’’