In a school library in Pontiac, Mich., sixth-graders are kneeling around a figure lying on the floor. The body isn't moving. What's going on here?

The body is a special plastic dummy the students are using as they practice a new-found skill: cardiopulmonary resuscitation, or CPR. The word "cardio" refers to the heart; "pulmonary" refers to lungs. "Resuscitate" means to revive, or reawaken. So cardiopulmonary resuscitation means heart and lung revival. And that's just what CPR is. The emergency first-aid procedure can revive someone who has passed out after a heart attack or injury.

In a CPR course, students learn to recognize the signs of a heart attack. They know that a serious heart attack can make a person fall down as if he has been shot. The victim may appear to have died -- but his life can be saved if someone nearby knows what to do.

An 18-year-old hardware store clerk in Virginia knew what to do. When an 82-year-old woman who was buying a flashlight collapsed in the store where he worked, Danny Treu started the CPR techniques he had learned in health class at school. It worked. After 15 heart compressions -- rhythmic pushing on the chest -- and some mouth-to-mouth resuscitation, the woman started breathing again. By that time, an ambulance had arrived, and Danny had saved a life.

In CPR classes, students learn how to do heart compressions. The rhythmic pressure imitates the body's normal heart beat, and sends blood flowing through the body. Students also learn how to give mouth-to-mouth resuscitation to imitate normal breathing. These methods provide the body with the oxygen it needs to survive. Often, the emergency techniques stimulate the heart and lungs enough to get them working again on their own.

CPR courses teach people the basics of emergency medicine. But remember, CPR is no substitute for medical care -- although it can keep a person who has been injured or has had a heart attack alive until professional help arrives.

The number of deaths from heart disease has decreased over the last 20 years. But this health problem is still a major killer, causing thousands of deaths every year. Experts say that many people who have heart attacks -- somewhere between one-third and one-half of them, in fact -- could be saved if they received CPR immediately.

It's important to learn CPR from a trained instructor who can show you how to do it, not just from reading a book or an article. If you would like to know more about CPR, contact the Red Cross or your local American Heart Association.

Around the country, thousands of adults and high-school students have taken CPR courses taught by qualified Red Cross or American Heart Association instructors. But until lately, few children learned CPR.

Doctors and health educators already teach kids about how to reduce the risk of getting heart disease. Most young people know that they should get regular exercise, eat a balanced diet, avoid getting overweight, and never smoke cigarettes. "The next step is is to train young people in CPR techniques," says Dr. Joseph Zanga, chairman of the American Academy of Pediatrics Committee on School Health.

This spring, the American Academy of Pediatrics, a group of 28,000 physicians concerned about children's health, recommended that students in grades 8 through 12 receive CPR training from instructors certified by the American Red Cross or the American Heart Association. Such programs can save lives. State officials from Nebraska report that high-school-age CPR experts have saved more than 1,000 people. In Nebraska, almost all the high schools already teach CPR to students who volunteer for the course.

Wait a minute -- those kids in Pontiac, Mich., are only in the sixth grade. Aren't they too young to learn CPR? Nurse Maggie Franckowiak and her husband Charles, a doctor, don't think so. They have designed an experimental CPR program called "Kids Add Life." They worked on the program for six years. This spring, 1,350 elementary age children in one Michigan school district began to learn CPR and related health information. The program is supported by the Michigan affiliate of the American Heart Association. After a year, experts will evaluate the program to see if it should be used in other school systems. Maybe you'll be learning it in your school one of these days. Tips for Parents

Nearly every community in the United States offers CPR instruction. Classes take place in hospitals, churches, businesses -- and, at least in the District -- firehouses. In Washington, the American Heart Association sponsors free "Heartsaver" classes at District of Columbia firehouses on the fourth Saturday of each month. To register, call 337-6400. For information on programs in Virginia or Maryland, call these local American Heart Association affiliates: in Montgomery County: 229-8100; in Prince George's County: 277-5116; in Northern Virginia: 941-8500. Knowing CPR ought to be part of every family's first-aid arsenal.