A national study of 2,269 women at 10 major medical centers suggests that women over 40 who take estrogen pills have sharply lower death rates and particularly low rates of heart disease, according to a preliminary finding.

The death rate among women taking the female hormone estrogen was only two-thirds that of similar women who were not taking the pills, according to a study at 10 major medical centers of women, aged 40 to 69, who were followed for an average 5.6 years.

The doctors and scientists who made the study published today in the Journal of the American Medical Association stress that they are far from ready to recommend any pills to increase women's life spans.

But they say they think it possible that they have confirmed the theory that it is women's natural estrogens--the most important female sex hormones--that protect them from heart disease, especially in younger years.

They say they think they have observed one way estrogens may do this: by increasing the women's store of high-density lipoproteins, or HDLs, a part of cholesterol that helps prevent heart attacks rather than causing them.

The government's National Heart, Lung and Blood Institute will convene a special workshop next fall to examine the new information and plan further research.

Women at all ages have less heart disease than men. But heart disease is the leading cause of death in women over 45. By ages 55 to 64, coronary heart disease kills nearly 200 women per 100,000 each year, and widespread cigarette smoking among young women is expected to increase this toll.

The women studied were among more than 60,000 men and women examined between 1971 and 1976 in a nationwide investigation of heart and blood vessel diseases sponsored by the National Institutes of Health.

They fall into three groups: those getting estrogens to relieve menopause symptoms, those getting "replacement estrogens" after hysterectomies and those getting estrogens because their ovaries were removed.

Seventy-two of the 2,269 women died during the study period. Their overall death rate was just 37 percent of that in comparable women not taking estrogens. The risk of death in the sub-group with still intact wombs and ovaries--those getting estrogens just to relieve menopause problems--was only 54 percent of that of comparable women.

In the early 1970s, from a third to half of all American women past mid-years took estrogens to relieve the hot flashes and other problems of menopause, which sometimes include osteoporosis or serious bone loss. However, doctors discovered that the estrogens increased their risk of endometrial cancer (cancer of the womb's lining) by up to 15 to 20 times, and now only 13 percent of post-menopausal women take estrogens, by one estimate.

Cautious doctors are now using the estrogens differently--in smaller doses, intermittently and supplemented with another hormone, progesterone--according to Dr. Donald Austin, head of the California tumor registry and a leading authority on cancer and estrogens. As a result, he said, endometrial cancer incidence has dropped back to that of pre-estrogen days.

"We can't yet be sure that it was taking estrogens that protected our women against heart disease," Dr. Basil Rifkind, chief of the heart institute branch dealing with lipids (blood fats) and heart disease, said yesterday. "This is the best explanation we have, and since the estrogen use also increased HDL cholesterol, it is reasonable to expect that it might help protect against heart disease. But we still have to rule out other possible explanations."