Students would not have to stop enjoying trans-fatty French fries and cookies in school cafeterias under a trans fat ban proposed by the city on Tuesday, although school officials yesterday said they are voluntarily eliminating the unhealthy ingredient from school menus.

“We’re working on our own to get it down,” the chief executive of School Support Services, Marty Oestreicher, said, adding that even though public schools were excluded from the trans fat ban, “we’re not taking that as an out.”

In the next two months, Mr. Oestreicher said the oil containing trans fat that schools chefs use to fry potatoes would be replaced with a healthier version.

Trans fat is made from adding hydrogen to vegetable oil, turning the liquid oil into a solid, which increases the shelf life of food but also increases the risk of coronary heart disease in people that consume it. On Tuesday, the Bloomberg administration announced a proposal to ban trans fat in foods served in city restaurants.

Currently, school cafeterias serve five different kinds of fried potatoes, including shoestring and wedge, with amounts of trans fat exceeding the Department of Education’s self-imposed 0.5-gram limit in entrée items. Mr. Oestreicher said the department was encouraging school chefs to serve baked potatoes as an even better alternative than the new oil.

“We don’t really serve French fried potatoes anymore,” he said.

Desert items are allowed a little more trans fat, 1 gram, and packaged items such as Linden’s cookies are exempt. Even so, the city has been in ongoing negotiations with Linden’s cookies to find a recipe without trans fat that children will enjoy.

“We work with the kids,” said Mr. Oestreicher. “We ask, ‘Does it taste okay?'”

Nutritional information for school menu items is listed by the Department of Education on its Web site, but does not say whether items contain trans fats.

Advocates for healthier school lunches praised the city for its efforts to improve school lunches.

“They’re so huge and it takes time,” director of the New York Coalition for Healthy School Lunches, Amie Hamlin, said. “They’re going in the right direction.”

The author of the book “Lunch Lessons,” Ann Cooper, known as the Renegade Lunch Lady for her national campaign to improve school food, said the city should be aiming to ban trans fats altogether in schools, not just restaurants.

“You still can serve kids without serving them food that makes them sick, ” Ms. Cooper said. “I don’t serve French fries and cookies, and my kids still eat.”