A government panel yesterday recommended new, more restrictive guidelines for treating people with high blood cholesterol levels. Based on these new guidelines, one in four adults -- some 40 million people adults -- are candidates for diet changes and, in more severe cases, for drug therapy.

"Medical practice will undergo a major change based on this report," predicted Dr. DeWitt S. Goodman, chairman of the panel that wrote the report.

Under the new guidelines, released by the National Cholesterol Education Program, an arm of the National Heart, Lung and Blood Institute, blood cholesterol levels below 200 milligrams per deciliter are considered "desirable." Those 200 to 239 mg are classified as "borderline high cholesterol," while those 240 mg and above are considered as "high blood cholesterol."

For the first time, guidelines also set levels for low-density lipoprotein (LDL) -- a cholesterol-carrying substance considered the major villain in the cholesterol-heart disease connection.

Blood levels of LDL of 160 milligrams or greater are classified as being at "high risk," 130 to 159 mg are considered at "borderline high risk," and less than 130 mg is classified as "desirable."

Reaction to the new guidelines was generally favorable, but at least one committee member, Dr. Stephen Havas, deputy commissioner of the Massachusetts Department of Public Health, called the guidelines "more confusing than is needed." Havas said testing LDL levels could cost $1 billion a year.

Cutting down on fat, particularly saturated fat, and lowering dietary cholesterol, "is the primary approach to treating patients with high blood cholesterol," Goodman said. "We think most patients can be treated by diet alone."

This means, the guidelines say, limiting fat to 30 percent of total calories by cutting back on fried foods, butter, margarine and whole milk dairy products, including cheese and other foods. It also means eating poultry without the skin and trimming all visible fat from meat, and the panel recommended limiting dietary cholesterol to 300 milligrams a day. Should these measures not lower cholesterol, additional reductions of saturated fat and cholesterol are recommended.

If after six months these second-step dietary changes have failed to lower blood cholesterol, then the government panel advised that drugs be used, beginning with cholestyramine and colestipol (two bile acid drugs) and nicotinic acid -- the vitamin niacin. --