A scientific panel's finding that healthy Americans need not lower the amount of fat and cholesterol in their diet was welcomed by milk, meat and egg producers yesterday but caused some chagrin at the American Heart Association.

"This is rare good news," said Patrick Healy, secretary of the National Milk Producers Federation.

"It was a surprise. It certainly was," said a spokesman for the American Heart Association -- who interrupted the conversation to tell his secretary to hold the cheese off his roast beef sandwich.

The report of the Food and Nutrition Board of the National Academy of Sciences, which was released Tuesday, flies in the face of previous guidelines, such as those issued in February by the Agriculture and Health, Education and Welfare departments and those formulated in 1977 by the Senate Select Committee on Nutrition and Human Needs.

Those recommendations, and the American Heart Association's guidelines, exhort Americans to lower their cholesterol and fat intake in the hope of preventing heart disease and stroke.

But the latest report -- while it favors lowering fat intake, especially saturated fats, for people at high risk of heart disease and those trying to lose weight -- states that the majority of Americans "probably have no need to reduce the fat level of their diets below 40 percent of calories," which is the proportion in the average American diet.

And it declines to make recommendations about cholesterol intake for healthy people, saying there is no evidence that changing one's diet can lower a high cholesterol level in the blood, which is one risk factor for heart disease.

The report was prepared following a National Institutes of Health request that the Food and Nutrition Board take action on "the flood of dietary recommendations currently being made to the American public."

Many of its conclusions echo standard advice on diet: maintain ideal body weight, avoid fat diets and eat a variety of foods.

It also recommends that Americans cut their salt intake from 10 to 3 grams a day, theorizing that such a reduction would be harmless and reduce the risk of high blood pressure.

But it does not advocate a similar reduction in fat, stating that research studies in which thousands of middleaged men were on low-fat diets showed only marginal decreases in heart disease and no decrease in death rate.

Audrey Cross, coordinator for human nutrition policy at the Department of Agriculture, said the Food and Nutrition Board looked at the same studies that USDA experts did, yet came up with the opposite recommendation about the fat intake.

Dr. William Kannel, professor of medicine at Boston University and head of the Framingham Study that first produced evidence on the relation of lifestyle to heart disease, said the latest report was inconsistent in its recommendations.

He argued that the idea of lowering fat intake to reduce heart disease is backed up by more evidence than is the idea of lowering salt intake to reduce high blood pressure. Since the board recommended the latter, he said, they should have recommended the former as well.

"It makes me wonder . . . at their objectivity," he said.

Food producers associations were delighted by the report. "We think it's really positive," said Christine Bushway, director of nutrition for United Egg Producers. The report is "welcome indeed," said Manly Molpus, president of the American Meat Institute.

"It stinks. It reads as if it was written by the meat, dairy and egg industries," said Michael Jacobson, director of the Center for Science in the Public Interest.

Jacobson charged that some of the report's authors are consultants to the food industry.