The city health department unveiled a proposal Tuesday that would bar cooks at any of the city's 24,600 food service establishments from using ingredients that contain the artery-clogging substance, commonly listed on food labels as partially hydrogenated oil.

Artificial trans fats are found in some shortenings, margarine and frying oils and turn up in foods from pie crusts to french fries to doughnuts.

Doctors agree that trans fats are unhealthy in nearly any amount, but a spokesman for the restaurant industry said he was stunned the city would seek to ban a legal ingredient found in millions of American kitchens.

"Labeling is one thing, but when they totally ban a product, it goes well beyond what we think is prudent and acceptable," said Chuck Hunt, executive vice president of the city's chapter of the New York State Restaurant Association.

He said the proposal could create havoc: Cooks would be forced to discard old recipes and scrutinize every ingredient in their pantry. A restaurant could face a fine if an inspector finds the wrong type of vegetable shortening on its shelves.

The proposal also would create a huge problem for national chains. Among the fast foods that would need to get an overhaul or face a ban: McDonald's french fries, Kentucky Fried Chicken and several varieties of Dunkin' Donuts.

Health Commissioner Thomas Frieden acknowledged that the ban would be a challenge for restaurants, but he said trans fats can easily be replaced with substitute oils that taste the same or better and are far less unhealthy.

"It is a dangerous and unnecessary ingredient," Frieden said. "No one will miss it when it's gone."

A similar ban on trans fats in restaurant food has been proposed in Chicago and is still under consideration, although it has been ridiculed by some as unnecessary government meddling.

The latest version of the Chicago plan would only apply to companies with annual revenues of more than $20 million, a provision aimed exclusively at fast-food giants.

A few companies have moved to eliminate trans fats on their own.

Wendy's announced in August that it had switched to a new cooking oil that contains no trans fatty acids. Crisco now sells a shortening that contains zero trans fats. Frito-Lay removed trans fats from its Doritos and Cheetos. Kraft's took trans fats out of Oreos.

McDonald's began using a trans fat-free cooking oil in Denmark after that country banned artificial trans fats in processed food, but it has yet to do so in the United States.

Walt Riker, vice president of corporate communications at McDonald's, said in a statement Tuesday that the company would review New York's proposal.

"McDonald's knows this is an important issue, which is why we continue to test in earnest to find ways to further reduce (trans fatty acid) levels," he said.

New York's health department had asked restaurants to impose a voluntary ban last year but found use of trans fats unchanged in recent surveys.

Under the New York proposal, restaurants would need to get artificial trans fats out of cooking oils, margarine and shortening by July 1, and all other foodstuffs by July 1, 2008. It would not affect grocery stores. It also would not apply to naturally occurring trans fats, which are found in some meats and dairy.

The Board of Health has yet to approve the proposal and will not do so until at least December, Frieden said.

The U.S. Food and Drug Administration began requiring food labels to list trans fats in January.

Dr. Walter Willett, chairman of the Department of Nutrition at the Harvard University School of Public Health, praised New York health officials for considering a ban, which he said could save lives.

"Artificial trans fats are very toxic, and they almost surely causes tens of thousands of premature deaths each year," he said. "The federal government should have done this long ago."