Knowing your blood cholesterol level will be as routine as knowing your blood pressure, and maybe even as familiar as knowing your body weight, if the National Heart Lung and Blood Institute has its way.

The NHLBI, part of the National Institutes of Health, will begin a new, nationwide program Friday designed to raise the public's consciousness about blood cholesterol and, doctors hope, lower the incidence of cardiovascular disease -- the country's number one killer.

Patterned after a similar health program that's been teaching Americans about high blood pressure for the past 16 years, the cholesterol program is designed "to urge the public to have their cholesterol levels checked, to know their cholesterol levels and to understand the implications of their cholesterol reading," says Dr. Claude Lenfant, NHLBI director.

The idea is to identify those Americans with high blood cholesterol levels. Estimates are that millions of Americans "are at an unacceptable risk of coronary disease because of blood cholesterol levels," Lenfant says.

Researchers believe a 10 percent across-the-board reduction in cholesterol will save about 100,000 lives a year. Such a reduction is the major goal of the project.

Although the average blood cholesterol level in the United States runs about 215 milligrams, approximately 25 percent of men and 30 percent of women have levels above 240 mg, the National Center for Health Statistics reports.

Last year, an NIH consensus conference on lowering cholesterol to prevent heart disease concluded that "it is a goal to encourage reduction of the blood cholesterol to approximately 180 mg for adults under the age 30 years and to approximately 200 mg for individuals age 30 or older."

Making those reductions requires changes in life style, including cutting back on dietary fat (to 30 percent or less of total calories), decreasing cholesterol (eating no more than 300 mg a day), and increasing exercise to raise levels of a protective form of blood cholesterol known as high-density lipoprotein, or HDL.

For some -- those with either exceptionally high blood cholesterol levels (240 mg and above) or those who don't respond to dietary changes -- it will also mean instituting drug therapy to lower blood cholesterol to safer levels.

Numerous studies have shown that the higher the cholesterol levels, the greater the chance of developing heart disease. The most recent evidence, presented this week at the American Heart Association's annual meeting, suggests that this relationship is true regardless of other well-known risk factors, such as cigarette smoking and high blood pressure. Findings from the Multiple Risk Factor Intervention Trial (MRFIT), a study of more than 350,000 men between the ages of 35 and 57 years, showed that the risk of fatal coronary disease increased as the cholesterol level increased, beginning with blood levels as low as 182 mg. There was a "strong and unequivocal relationship of serum cholesterol to risk, for both cigarette smokers and nonsmokers, for both men with normal blood pressure and high blood pressure," says Dr. Jeremiah Stamler, a coordinator of the MRFIT study. "This relationship held consistently, systematically and without contradiction . . . from 182 mg on up."

One of the major goals of the National Cholesterol Education Program will be to encourage people to know their blood cholesterol by having it checked. Some 65 percent of Americans reported in 1983 that they have never had their cholesterol level measured, reports the Cholesterol Awareness Project.

Without a blood test, people with high blood cholesterol levels have no way of knowing they are at risk, until there is a major health problem such as a heart attack, stroke or clogged arteries requiring bypass surgery.

"The majority of people don't know that they are a time bomb," says Dr. Basil Rifkind, chief of lipid metabolism and atherogenesis at NHLBI.

Two new -- and quick -- laboratory tests may change all that. Until recently, measuring blood cholesterol meant drawing about five milliliters, about a teaspoon, of blood and then waiting a minimum of several hours for the results. "A physician would say to patients, 'Come back when I've got the results,' " explains Rifkind. Because of busy schedules, that time lag often translated to a couple of weeks later.

But these new tests give results in minutes, in some cases while a patient is still in the doctor's office. They also require far less blood. One of the tests, by Boehringer Mannheim Diagnostics, uses only one drop; another by Kodak uses 300 microliters.

These new tests also cost much less than $8 to $25 charged for the conventional methods. The Boehringer Mannheim test is done for about 66 cents; Kodak's runs about $1.40. Both tests, Rifkind says, make it "as easy to measure blood cholesterol as it is to measure blood pressure." Knowing about blood cholesterol levels is the first step toward meeting the new national goals, Lenfant and other experts say. The hope is to make the National Cholesterol Education Program as successful as the National High Blood Education Program, a program credited with helping to reduce the incidence of stroke by some 45 percent in the past 16 years.

As Mount Sinai's Dr. Virgil Brown put it at a recent planning meeting of the National Cholesterol Education Program: "Once people know their blood cholesterol and have information on how to deal with this, I think we're going to see, in general, cholesterols coming down across the country, and I think the effects are going to be as dramatic as the blood pressure effects have been, which are terribly heartening to me. Resources

Among the sources that offer additional information on cholesterol are:"Cholesterol Counts," a pamphlet designed to teach health professionals how to help their patients lower blood cholesterol, and "Fact Sheet on Blood Cholesterol," describing cholesterol basics. Both are free. Write: Box C, National Heart Lung and Blood Institute, Building 31, Room 4A21, Bethesda, Md. 20892."The Rutgers Guide to Lowering Your Cholesterol," by Hans Fisher, PhD, and Eugene Boe (Rutgers University Press; $16.95)."The Living Heart Diet" by Dr. Michael DeBakey, Dr. Antonio Gotto, Lynne W. Scott and John P. Foreyt (Simon & Schuster $19.95)."The American Heart Assocation Cookbook," (David McKay Company, Inc., $12.95).