WASHINGTON (AP) - The government is moving to require the listing of artery-clogging trans fat on food labels after a report from the Institute of Medicine found there is no safe level in people's diets.

Eating some trans fat may be unavoidable, but people should reduce their intake as much as possible to lower the chance of heart disease, the Institute, a branch of the National Academy of Sciences, said Wednesday.

The Food and Drug Administration has been developing rules to require listing of trans fat on food labels. FDA food labeling chief Christine Lewis Taylor said her agency would act as soon as possible.

The final rule could be issued sometime between next fall and early spring, Taylor said in a telephone interview.

Because it is directly associated with the bad LDL cholesterol and heart disease, there is no safe amount of trans fat in the diet, the Institute of Medicine said in its report.

But since trans fat occurs in meat, dairy products, pastries and many other foods, eliminating it would mean such extraordinary changes in diet for many people that they might not get enough protein or nutrients, the Institute added.

Because it considers no amount safe, the Institute declined to list an upper limit for trans fat in the diet. It's that limit that FDA uses to establish the recommended daily value for any part of the diet.

That means the FDA will require food producers to list the grams of trans fat on the label with other nutrition facts, but it will not include the percent of daily value, Taylor explained.

The private Center for Science in the Public Interest has been pressing for inclusion of trans fat on labels since 1994.

``This is the first attempt by a panel of experts to set a safe intake for trans fat ... what's surprising is they concluded the only safe intake of trans fat is zero,'' said Margo Wootan, director of nutrition policy at CSPI.

She suggested a combined listing of trans fat and saturated fat with a combined daily upper limit. Both types of fat have been shown to contribute to heart disease.

``If trans fat was labeled separately people might go to great lengths to eliminate it, and maybe they would increase their intake of saturated fat and that would be bad,'' Wootan said.

Taylor agreed there are lots of reasons to be worried about both those fats in the diet, but said they won't be combined on the labels. There will be a separate line for trans fat.

Rather that trying to recommend a limit on consumption of trans fat, the IOM report said it should be ``as low as possible while consuming a nutritionally adequate diet.''

The FDA has previously estimated that listing trans fat on food labels would save between 2,000 and 5,600 lives a year as people either chose healthier foods or manufacturers improve their recipes to leave out this fat.

Currently the only way to determine if a food contains trans fat is to look for ``hydrogenated'' on the ingredient list. The most common source of trans fat is partially hydrogenated vegetable oil, in which liquid oil is turned into a solid. This material is included in thousands of foods. Typically, the harder a margarine or cooking fat, the more trans fat it includes.

The National Academy of Sciences is an independent organization chartered by Congress to advise the government on scientific matters.

On the Net:

Institute of Medicine: http://www.iom.edu

Food and Drug Administration: http://www.fda.gov

Center for Science in the Public Interest: http://www.cspinet.org