For the modern American seeking ways to avoid a heart attack, exercise can be given rather low priority, new research indicates.

While exercise is good for you -- at least if you are male -- the lack of it is only a "minor risk factor" for heart disease compared to smoking, high blood pressure of obesity, the study shows.

"Just throw your cigarette pack away and you've done more than all that jogging -- and you don't have to get bitten by your neighbor's dog, run over by a bus or shot by a cop," said Dr. William B. Kannel, professor of medicine at Boston University.

Kannel is codirector of the Framingham Study, a monitoring of 4,000 residents of Framingham, Mass., that has been going on since the 1950s.

Results of that study, he said,indicate that while a sedentary life poses some increased heart attack risk for men, other factors are far more important.

And for women, there is no added risk, he said.

Activity patterns of healthy Framingham subjects were first recorded, along with other information in the 1950s, long before jogging swept the country, Kannel said. Their exercise levels have been reassessed in the past 10 years, but the subjects are now 60 to 90 years old and have remained a "sedentary population," he said. So while statistics compare the benefits of moderate activity against none, they cannot assess the value of a long-term systematic exercise program.

Other studies have shown that exercise can alter other, more important risk factors such as obesity, and possibly even raise levels of a blood chemical called high-density lipoprotein, which is thought to protect against heart disease.

Kannel called exercise an important part of a comprehensive health program. "You don't see many fat, smoking joggers," he said.

But no one knows that level of exercise is most beneficial, and too-vigorous exercise may have risks, he said. Research has concentrated on incidence of heart disease in people with various activity levels, but has not measured the value of physical fitness, in which a person's heart beats more slowly and his blood carries more oxygen because of constant conditioning.

Although at the time the Framingham subjects were first studied none had obvious heart disease or other illness, Kannel questioned whether a desire to exercise might not be an indication of better health, which would bias the study's results.

Perhaps, he said, vigorous people exercise, while others do not because of hidden ill health.