The world's No. 1 hamburger chain said on Wednesday it is going to start listing calorie information on menus in some 14,000 U.S. restaurants and drive-throughs - ahead of a national rule that will require larger restaurant chains to make such disclosures.

McDonald's Corp (MCD.N) is a trend setter for restaurants and its move in this arena - while prompted by regulations and pressure from public health activists - is likely to force other restaurant operators to follow quickly.

The state of California and cities like New York already require that calories be clearly listed on menus. Under the new U.S. healthcare law, restaurants across the country must soon put calorie counts and other nutrition details on menus.

The national rules target restaurants with 20 or more locations, as well as other retail food outlets. Most major chains have resisted posting such information, without legislation and the threat of fines.

The date for national compliance has been delayed and is not expected to be set until after the U.S. presidential election.

McDonald's was slow to warm to calorie labeling.

When labeling proposals were gaining steam several years ago, McDonald's representatives publicly opposed them. A common complaint was that rules from one jurisdiction to another were inconsistent. Some officials also said calorie disclosures would violate customer privacy.

Cindy Goody, senior director of nutrition for McDonald's USA, described the company's latest move as a way to help its customers understand their food choices.

The company, which is in nearly every U.S. community and serves 25 million U.S. customers daily, is casting the nutrition disclosures as a business opportunity.

"It's a new reason to visit more often," Goody said.

Calorie and other nutrition information already is available on the company's website. Listing calories on menu boards allows customers to use that information when they are making a decision about what to eat.

Margo Wootan, the director of nutrition policy for the nonprofit Center for Science in the Public Interest, thinks the national calorie labeling deadline will probably be around the end of 2013 - so customers at McDonald's will be getting the information about a year earlier than what will be required.

Disclosure rules already have helped convince many restaurants, including Starbucks Corp (SBUX.O), to cut calories from their food and to highlight healthy options, she said.

Those moves matter because Americans get about one-third of their calories from eating out, Wootan said.

Amid demands from parents and health activists, McDonald's also has taken steps to make menu items healthier.

It tweaked its popular Happy Meals for children - reducing the french fries portion by more than half and adding apples to every order.

This past summer, it rolled out a "Favorites Under 400" menu that highlights products in that calorie range.

McDonald's also plans to add more fresh fruits and vegetables to its menu and has set a goal of decreasing calories, saturated fat and added sugars across its U.S. menu by 2020.

Corporate Accountability International has been pressing McDonald's to make bolder changes to its menus and to stop advertising to children.

"To truly address its health impact ... the burger giant (needs) to make more fundamental, far-reaching changes," said Juliana Shulman, senior organizer for the group's Value the Meal campaign.

More than two years ago, Panera Bread Co (PNRA.O) became the first national restaurant chain to voluntarily post calories at company-owned stores. Sandwich chain Subway has used calorie disclosures to position itself as a healthier alternative to rivals like McDonald's and Burger King Worldwide Inc (BKW.N).

McDonald's shares were down $0.30 at $90.90 in midday trading on the New York Stock Exchange. (Reporting By Lisa Baertlein in Los Angeles; Editing by Jeffrey Benkoe, Leslie Adler and Dan Grebler)

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