A prominent National Institutes of Health panel concluded yesterday that high levels of cholesterol in the blood cause heart disease and that scientific studies show "beyond a reasonable doubt" that lowering cholesterol levels, preferably through diet, will reduce the risk of heart attacks.

The 14-member advisory group suggested that most Americans change their dietary habits to achieve a national goal of an across-the-board 10 percent reduction in blood cholesterol. Such a reduction, it said, could save 100,000 lives a year, reducing deaths from heart disease, the United States' No. 1 killer, by one-fifth.

"We think all Americans are at unnecessarily high risk of heart disease largely because of the kind of diet we eat," said panel chairman Dr. Daniel Steinberg of the University of California, San Diego.

The panel, a diverse group of researchers, physicians and nonscientists, endorsed a diet that would draw only 30 percent of its total calories from fat, rather than the current 40 percent. It also recommended that less than 10 percent of daily calories come from saturated fat and that cholesterol intake be reduced to 250 to 300 milligrams a day. A single egg yolk has about 270 milligrams of cholesterol.

The panel, which found that more than half of Americans have undesirably high blood cholesterol levels, also set new guidelines for physicians, suggesting more vigorous treatment for the one-fourth of adult men and women who are considered at moderate to high risk of developing heart disease.

Steinberg emphasized that the preferred treatment was dietary change. The panel suggested the use of cholesterol-reducing drugs mainly for the 10 percent who are at highest risk and for whom a dietary change proves inadequate to reduce cholesterol levels.

"We do not want anybody to take any drug therapy except as a last result to achieve the end," he said.

The advisory group also urged the government to launch a national education effort, recommended that the food industry develop and market foods that will make it easier for people to modify their diet, and called for food labeling to indentify a product's fat content, type of fat and cholesterol level.

The advisory panel was established by the National Heart, Lung and Blood Institute and the NIH Office of Medical Applications of Research, which were looking for definitive, practical advice that might put an end to the long-running debate about cholesterol.

Steinberg said the recommendations represented a "unanimous" view of the panel, backed by the "large majority" of research opinion.

The American Heart Association has promoted the same kind of diet suggestions for many years. But the NIH panel went further, setting up moderate- and high-risk treatment categories that would prod physicians and patients to pay more attention to blood cholesterol levels.

"Until now the average physician has been confused and uncertain. Now they don't have that excuse anymore," the panel chairman said in an interview.

As a "realistic" goal, the panel encouraged reduction of blood cholesterol to about 180 milligrams per deciliter (mg/dl) for adults under 30 and about 200 mg/dl for those who are older. Available data generally suggests that levels above 200 to 230 mg/dl mean an increased risk of heart disease.

The panel report noted that high blood cholesterol, cigarette smoking and high blood pressure are the three major risk factors for heart disease. The risk is greatest in men and increases with age.

Most coronary heart disease is a result of hardening of the arteries, or atherosclerosis, a progressive disease in which excessive fats and cholesterol in the blood clog the inner walls of these vessels. When a blood clot gets stuck in a narrowed artery, a heart attack can result.

Cholesterol is produced naturally in the body and in low levels is a crucial part of cell functioning. Though some people are genetically predisposed to build up higher levels in the blood, cholesterol levels also are influenced by diet.

Steinberg noted that eating less saturated fat -- the kind of fat highest in red meats and dairy products -- would have the greatest impact on reducing blood cholesterol. This can mean eating more fish, poultry and lean meat.

Cutting back on foods high in cholesterol is also important, he said. Cholesterol is found only in animal foods and is highest in beef kidney, liver and egg yolk. Although cholesterol consumption has been declining in recent years, government statistics show that average daily intake still ranges between 300 and 500 milligrams.

Panel member Richard Carleton, a Brown University cardiologist, emphasized that the recommended heart diet meant a "cultural change" in the American approach to eating but not a "prescribed diet. We are recommending good, healthy and very tasty nutritious eating."