The Food and Drug Administration proposed yesterday that consumer food labels list the amount of trans fatty acids, a type of fat that significantly increases the risk of heart disease.

The FDA proposal is expected to change consumer behavior and to prompt food companies to reduce the amount of trans fatty acids in foods. The combination is projected by the FDA to prevent 6,400 cases of heart disease each year, including at least 2,100 deaths.

While it will take at least three years for the benefits to accrue, "we think that the total savings over a 20-year period is $20 billion," said Joe Levitt, director of the FDA's Center for Food Safety and Applied Nutrition. "That's very sizable from just this one change alone."

Also known as hydrogenated fat, trans fatty acids are used by the food industry to increase shelf life and flavor in a wide variety of products, including fast-food french fries, crackers, cookies, snack foods and some margarines.

A growing number of scientific studies link trans fatty acids to premature heart disease. Like saturated fat, trans fat hikes blood levels of the harmful cholesterol known as low-density lipoprotein (LDL), an important contributor to heart disease.

But consumers have been in the dark about how much trans fat they ate because food manufacturers were not required to list the fat separately on labels. Trans fat was considered, however, in the calculation of total fat.

Because many foods contain as much trans fat as saturated fat, "people are getting twice the artery-clogging fat that they think they are," said Margo Wootan, senior scientist at the Center for Science in the Public Interest, which began petitioning the FDA in 1993 to amend the food label regulation to include trans fat along with saturated fat and total fat.

Under the proposed regulation, trans fat will be included in the same listing as saturated fat. When trans fat is present in a food, an asterisk or other symbol will follow the saturated fat listing and will direct the consumer to a footnote that will state how many grams of trans fat are in the food.

The FDA proposal also defines "trans fat free" foods, which must contain less than 0.5 grams each of trans fat and saturated fat. Trans fat will be considered as well in labeling foods as "lean" or "extra lean," or as "reduced saturated fat" or "low saturated fat." Under the proposal, low-cholesterol claims on foods will be permitted only when products contain less than 2 grams of saturated fat and trans fat combined.

Listing trans fat on food labels "will provide consumers with important information that they can use to decrease their risk of coronary heart disease," the FDA's Levitt said.

But some fear that the changes will only confuse consumers. "This is one more thing on the food label," said Connie Diekman, a national spokeswoman for the American Dietetic Association, which opposes the regulation. "We still haven't achieved the No. 1 goal of reducing total fat."

Many others, including the American Heart Association, the National Cholesterol Education Program and industry groups, said the change is long overdue. Heart disease is the leading cause of death in the United States, claiming some 500,000 Americans each year, according to the American Heart Association.

"Frankly, we welcome the proposal," said Richard Cristol, president of the National Association of Margarine Manufacturers, who noted that his competitors in the butter industry must now list trans fat on their labels too. "We think the consumer will recognize how heart healthy many margarine products really are."

The public has 90 days to comment on the FDA's proposed regulation.