Chain restaurants, convenience stores, concession stands and vending machines would soon have to display calorie information for the food products they sell under rules proposed Friday by the Food and Drug Administration.

“We do see this as an important step in providing consumers with information they can use in choosing healthy diets and fighting obesity,” Michael R. Taylor, deputy FDA commissioner for foods, said in describing the nation’s first federal menu-labeling law.

The rules, required by Congress in a little-noticed provision of the health-care reform law passed last year, are subject to a public comment period before they are finalized and implemented in 2012, Taylor said.

A notable exception under the proposed rules are movie theaters, which earn up to a third of their income from sales of popcorn and other items at their concession stands. Movie theaters have lobbied the FDA in recent months, saying they should not be subject to the law because people go to theaters to see movies, not to eat meals.

That means moviegoers at Regal Theaters, the country’s largest chain with 548 theaters, will not be confronted with the fact that a medium tub of unbuttered popcorn can contain 1,200 calories, according to a 2009 laboratory analysis ordered by the Center for Science in the Public Interest. That’s half the recommended total daily caloric intake for a 45-year-old man.

Under the regulations, any restaurant with 20 or more locations offering standard fare — including table-service establishments, fast-food outlets, bakeries and coffee shops — would have to disclose calories “clearly and prominently” on menus or menu boards, including drive-through order stations. Other nutritional information, such as sodium and fat content, would have to be available upon request.

Vending machines would have to clearly display the calorie counts for each item. The information must be in close proximity to the machine so that consumers can see the calories as easily as the price or selection button number, according to the FDA.

Food industry groups, which have been meeting with the FDA over the past year and have anticipated the rules, said a federal law is better than a patchwork of state and local regulations. Menu labeling laws have been passed in 18 states and localities, including Montgomery County, Md., California and New York City, and some restaurant chains already voluntarily provide the information.

Dawn Sweeney, president and chief executive of the National Restaurant Association, said her organization supported the federal law.

“From Portland, Oregon, to Portland, Maine, the new standard will help chain restaurants provide the same type of nutrition information to consumers in any part of the country,” she said.

With fewer outlets to absorb the cost, small- and medium-size chains may face the greatest burden of the new requirements as they analyze their fare to determine calorie counts, reprint menus and refashion menu boards.

In addition to movie theaters, the regulations would not apply to bowling alleys, airplanes and other places where less than half the floor space is devoted to food sales. But the rules would cover a chain kiosk housed inside another business — a Starbucks inside a bookstore, for example.

The Center for Science in the Public Interest, which has pushed for menu labeling for a decade, hailed the proposed rules but said that theaters and alcoholic beverages should have been included.

“If a movie theater is going to serve up thousand-calorie tubs of popcorn, 400-calorie drinks and 400-calorie boxes of candy, the least they could do is tell you about it,” said Margo Wootan, nutrition policy director for the group.

Rep. Rosa L. DeLauro (D-Conn.), who authored a separate bill requiring menu labeling, said Friday that she would “work to ensure that the final rule is strengthened” to include movie theaters and alcoholic beverages.

Patrick Corcoran, a spokesman for the National Association of Theatre Owners, a trade group, declined to comment Friday.

When Congress passed the health-care law, it stipulated that the labeling requirements should apply to restaurants and “similar retail food establishments.”

But in a nation where ready-to-eat food is seemingly everywhere — from refrigerated “grab and go” cases in drugstores to pizza franchises inside gas stations — the FDA has found it tricky to define “food establishment,” Taylor said.

And in restaurants where diners can customize their orders — deciding whether to add cheese or guacamole, or both, to a burrito, for instance — it’s difficult to display specific calorie counts. As a result, the FDA says restaurants can post a range of calories for items that are customized. “In a pizza situation, where you can have 20 different toppings, we’re allowing those calories to be declared in ranges,” Taylor said.

In supermarkets, all packaged foods have carried a “Nutrition Facts” label since 1990, allowing shoppers to quickly assess such information as calories, sodium and fat. But the same information has not been available at many restaurants, convenience stores and other places where food is sold.

“For people who are interested or curious, this will be staggering information,” said Marion Nestle, who teaches nutrition, food studies and public health at New York University. “And they’ll change their behavior. For others, it’s not.”

According to the USDA, Americans spent 42 percent of their food budgets in 2009 on items away from home, both for meals and snacks. And that comes at a cost to the waistline: When eating away from home, Americans consume more calories, fat and cholesterol, according to USDA researchers.

Still, some experts are skeptical that calorie information will cause people to make different choices.

“I think it will have an initial impact, but not a lasting impact,” said Bonnie Riggs, an analyst with the NPD Group, a market research company.

In research performed in December, NPD found that people perusing a hamburger restaurant’s menu chose foods with 12 percent fewer calories when they were provided the calorie counts for each item, ordering fewer french fries, regular soft drinks, onion rings and extra-large burgers.

But when asked how they choose restaurant food, Riggs said, they spoke about quality, freshness and portion sizes, among other things. “Calories weren’t even mentioned.”

Research editor Alice Crites contributed to this report.

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