Challenging one of the more popular notions of modern health care, researchers say they have found evidence that men with hard-driving "Type A" personalities are almost twice as likely to survive heart disease as those who are less aggressive.

The study also questions the theory that Type A behavior leads to a higher risk of getting heart disease, a theory that has led millions of Americans to change their life styles.

"The results really stunned us," said David R. Ragland, an epidemiologist at the School of Public Health at the University of California at Berkelely. "Changing Type A behavior may prove to have no beneficial effect and there is some evidence that it will even be harmful."

The study, which appears in today's issue of The New England Journal of Medicine, is certain to add fuel to the continuing debate over the health effects of the competitive and aggressive behavior that describes the Type A personality. In contrast, "Type B" personalities are described more often as patient and secure, rarely letting minor problems upset them.

Ragland and Richard J. Brand followed a group of 257 men of both personality types who were identified as having heart disease. Over a 13-year period, the Type A men were only 58 percent as likely as the others to die from heart disease.

Previous studies have suggested that behavior modification programs among Type A men who had suffered heart attacks would cut their risk of a second attack in half.

But the definition and importance of Type A behavior, and the relationship between personality and heart disease, have been disputed for more than 30 years. Many experts now say there is a complicated relationship, but they are not certain that rules can apply to groups of people.

"It might be that what is good for one person is disastrous for another when it comes to heart disease," Ragland said.

His study found that in the short term, Type A and Type B patients died of heart disease at the same rate. Among the 231 cases who survived for at least 24 hours, however, the mortality rate for the 160 Type A men was far lower than for the 71 Type B men.

The authors cite as one possible explanation that Type A survivors may respond much more forcefully to heart disease. They may be better at changing their diets and habits. And because Type A people are often considered leaders, they might have had a better ability to take charge of their medical situation.

In the past, those who believe in Type A theories suggested that the constant feelings of hostility and aggression harbored by Type A personalities led to the extra secretion of certain hormones. That, in turn, causes unacceptable increases in blood pressure and heart rate that can lead to coronary heart disease.

Recently, however, new research has challenged the traditional wisdom that Type A behavior would lead a person to an increased risk of heart disease. Doctors often disagree on how to measure Type A, how to treat it or whether it really exists.

In an editorial also published in today's New England Journal, Dr. Joel E. Dimsdale writes that the new research "presents such a startling conclusion that it is appropriate to reassess the legacy of studies on Type A behavior."

Although previous data from the Western Collaborative Group Study, which followed 3,154 healthy men for 8 1/2 years, provided support for the view that Type A men were at increased risk for heart disease, Dimsdale wrote that the current information "casts a long shadow indeed" over the entire theory.

But Dr. Meyer W. Friedman, who wrote the original research on Type A behavior and remains one of its most forceful believers, called the new research flawed.

"They did not classify the people properly," he said. "We have found very clearly that Type A behavior causes heart disease and that those who modify it are at reduced risk for heart attacks."