By Toni Clarke and Anjali Athavaley

Nov 24 (Reuters) - The U.S. government is set to publish sweeping new rules on Tuesday that will require chain restaurants to disclose calorie counts on menus, establishing a national standard that pre-empts the current patchwork of state laws and applies to restaurant chains with 20 or more outlets.

The new standards, which are part of the 2010 Affordable Care Act, were announced by the Food and Drug Administration and also apply to large vending machine operators.

Under the rules, calories must be displayed on all menus and menu boards. Other nutritional information - including calories from fat, total fat, saturated fat, trans fat, cholesterol, sodium, total carbohydrates, fiber, sugars and protein - must be made available in writing upon request.

"Obesity is a national epidemic that affects millions of Americans," FDA Commissioner Margaret Hamburg said on a conference call with reporters on Monday. "Strikingly, Americans eat and drink about a third of their calories away from home."

The final rule, unlike a proposal issued in 2011, includes movie theaters and amusement parks. It also includes alcoholic beverages served in restaurants, though not drinks mixed or served at a bar.

The agency said it made changes to its proposal after considering more than 1,100 comments from industry, public health advocates and consumers. It narrowed the scope of foods covered to clearly focus on restaurant-type food. Foods such as deli meat bought at a grocery store counter will be excluded.

The restaurant industry reacted positively to the changes.

"We believe that the Food and Drug Administration has positively addressed the areas of greatest concern," said Dawn Sweeney, chief executive of the National Restaurant Association, which represents 990,000 restaurant and food-service outlets.

Some companies already display calorie information. Panera Bread Co in 2010 became the first to voluntarily display calorie information at all its cafes nationwide. Others, including McDonald's Corp and Starbucks Corp, followed suit.

Foods covered by the new calorie rule include meals at sit-down restaurants, take-out food, bakery items, ice cream from an ice-cream store and pizza, which will be labeled by the slice and by whole pie. Seasonal menu items, such as a Thanksgiving dinner, daily specials and standard condiments will be exempt.

Hamburg acknowledged that calorie counts for pizza slices and many other foods made on the premises will vary and may not always be exact. Restaurants may draw on a variety of data-bases, cookbooks and food package labels to calculate the calorie counts.