Following seven simple health rules can extend a man's life by 11 years on the average and a woman's by seven, according to one of the nation's most significant public health studies.

Among 6,928 Californians who followed most of these rules during the years 1965 through 1974, there were far fewer deaths than expected. Men who followed no more than three of these rules died at nearly three times the rate of men who followed six or seven. Women who followed no more than three died at twice the rate of those who followed six or seven.

The seven health rules:

Do not smoke cigarettes.

Get some regular exercise.

Use alcohol moderately or not at all.

Get seven to eight hours of sleep nightly.

Maintain proper weight.

Eat breakfast.

Do not eat between meals.

These conclusions were published last week by Dean Lester Breslow and Dr. James Enstrom of the University of California at Los Angeles' School of Public Health. Breslow is an authority on practical steps to prevent illness.

In an interview, he called the study "one of the first large-scale demonstrations" of the association among ways of life, health and death.

In a separate analysis of the same group, Drs. James Wiley and Terry Camacho of the California Health Department conclude that probably only five of the health practices are crucial.

These, they say are: not smoking cigarettes, taking some physical exercise, getting seven to eight hours' sleep, avoiding overweight and drinking in moderation -- 17 to 45 alcoholic drinks a month -- rather than either excessive drinking or abstention.

The differences in interpretation are a matter of "looking at the statistics in different ways," Breslow said.

What is "really important," he said, is that "we believe we have shown" that people who observe all or virtually all these practices, "people who live moderate and regular lifestyles," really do improve their health and have a better chance, on the average, for long life.

Some people who follow all the rules do die early. But the California study -- a project of UCLA and the California Health Department's Human Population Laboratory -- clearly seems to have three main lessons: Following good health habits can pay. The more good habits, the better. Changing a bad habit to a good one, like stopping smoking, also pays.

The Health Department first surveyed the health habits of 6,928 Alameda County (Berkeley area) adults, a representative sample of all adults, in 1965. Drs. Nedra Belloc and Breslow published the first results in 1973.

The time-consuming new analyses, published in Preventive Medicine, take the group through 1974. By then, there were 6,246 survivors. Of these, 4,864 -- still a representative group, Breslow believes -- participated in the latest survey. Also, death certificates from California and other states were scrutinized to determine how many of the others had died.

When the California health scientists first said in 1973 that -- for men or women aged 45 -- following all seven habits lengthened life by several years, some skeptics said, in effect, "You may be way off. The people with the poorer sleep and eating habits may just be those who are ill and near death."

The fact that the same kind of results has held up over the years makes them far surer, Breslow said. Some other important points:

Breslow and Enstrom list "never" smoking as one of their optimum health habits. But Wiley and Camacho add that light-to-moderate smokers who quit smoking by 1965 showed the greatest improvement in health by 1974.

Breslow-Enstrom found both overweight and underweight to be unhealthy. Wiley-Camacho think obesity is the real danger, not modest underweight.

Some persons who preach physical activity say only strenuous exercise really helps. Wiley-Camacho find a "marked" difference in health between those who report no activity and those who report even a little, but no consistent trend showing better results for strenuous exercisers.

Breslow said "we can't be sure" about such details when "we break the larger group into sub-groups," because there aren't enough people in the sub-group -- light and heavy exercisers, for example.

What "we do get," he said, is a whole picture of how to be healthy.