Such vigorous exercise as jogging, swimming, tennis or chopping wood, performed regularly, may protect against as well as provoke sudden death from heart attack, but long-term health benefits of physical activity appear to outweigh the risks, according to a major study released today.

Its researchers, at the University of North Carolina and University of Washington, are the first to compare risks and benefits of exercise in the same population of healthy men, and their work may help resolve debate about the value of exercise.

That debate drew national attention this summer when runner and author Jim Fixx died of a heart attack while jogging.

The study, published in the New England Journal of Medicine, showed that risk of sudden death from cardiac arrest is greater during strenuous exercise. But it found that, in men who exercise regularly, the overall risk of dying at any time from cardiac arrest is reduced by 60 percent when compared with those who seldom exercise.

"For the first time, one study appears to resolve the apparent contradiction posed by the occurrence of deaths during exercise on the one hand and the burgeoning reports of the benefits of habitual exercise in coronary heart disease on the other," Drs. Paul D. Thompson of Brown University and Jere H. Mitchell of the University of Texas wrote in an editorial accompanying the study.

Conducted in Seattle and suburban King County, Wash., the study involved interviews with the wives of 133 men who had no known prior heart disease and collapsed from cardiac arrest.

Such arrest, a lack of pulse resulting from heart attack or other heart rhythm disruptions, usually causes death unless the victim is resuscitated in three to five minutes.

Interviewers asked what the men were doing at the time of the attack and their normal exercise levels. They found that nine suffered cardiac arrest while exercising; six survived after resuscitation efforts.

Men who exercised fewer than 20 minutes a week had a 56 times greater chance of cardiac arrest while exercising than while resting. More active men who exercised vigorously at least 2 hours and 20 minutes weekly had a five times greater risk of attack while exercising.

The study found that the overall risk of cardiac arrest among exercise enthusiasts was only 40 percent of that of their armchair counterparts.

It found that only about one of every 20,000 exercisers each year risks sudden death, researcher Dr. David S. Siscovick of the University of North Carolina said.

The editorial cautioned that vigorous exercise is not foolproof protection against heart disease, particularly in people with other signs of potential heart problems.

It noted that those with high risk of heart disease should check with physicians before undertaking exercise training and should not ignore discomfort during exercise.