Large U.S. chain restaurants, criticized for their role in the country's obesity epidemic, agreed on Wednesday to support legislation that would require them to disclose calories on their menus.

Chain restaurants with 20 or more locations would have to list on their menus the number of calories per item and would also have to make available upon request other nutritional information such as the amount of sugar, salt or cholesterol.

The menu labeling law could be included in health reform legislation expected to be discussed in Congress during the next few weeks.

"America is facing an obesity epidemic which must be addressed at the national level," said Republican Senator Lisa Murkowski, who along with Democratic Senators Tom Harkin and Tom Carper, have backed menu labeling legislation.

"This compromise will allow Americans to be informed about the nutrition content of their foods prior to the point of purchase," she said.

The measure is backed by the National Restaurant Association, which includes Dunkin Donuts and Darden Restaurants Inc, operator of the Red Lobster and Olive Garden chains. The American Diabetes Association and the Center for Science in the Public Interest also support the legislation.

"To have all of those key players at this point as one unified front to move forward with a national nutrition standard is, I think, really significant," said Sue Hensley, a spokeswoman with the National Restaurant Association.

Laws requiring that calories and other nutritional information be posted have become increasingly popular as states and cities struggle to combat the country's surging obesity problem while promoting health and nutrition.

About one-third of U.S. adults are obese, a condition that increases the risk of heart disease, diabetes, cancer and other medical problems.

Last September, California became the first U.S. state to require fast-food restaurant chains to list calories on their menus. Similar calorie information went into effect in New York City last year, and more than a dozen states are considering similar health code provisions.

The restaurant industry, which has conceded that change is on the way, has urged the federal government to establish a uniform nationwide approach — rather than a patchwork of local and state laws — detailing what information restaurants must provide.

A nationwide system would create a level playing field for all restaurants and better protect them from frivolous lawsuits, the restaurant association said.

Attempts to pass labeling laws since 2003 have stalled several times because of opposition by the Republican leadership and business groups.