More American women are being screened for breast cancer, but most still fail to get a mammogram as often as widely accepted guidelines suggest.

Fewer than a third of over-40 women follow mammography guidelines set by the National Cancer Institute, the American Cancer Society and other medical organizations, according to a new nationwide survey.

The survey found that 64 percent of women 40 and older had had a mammogram, or breast X-ray, up from 37 percent in a 1987 survey. But only 31 percent -- fewer than one in three -- followed the recommended schedule of one mammogram every year or two for women in their forties and one every year thereafter.

Conducted with help from NCI, the survey was commissioned by the Jacobs Institute of Women's Health, a nonprofit group founded by the American College of Obstetricians and Gynecologists. The results were reported by the federal Centers for Disease Control.

An estimated 44,000 American women will die this year of breast cancer, which kills more women than any other malignancy except lung cancer.

Early detection improves the chance of successful treatment. Previous studies have indicated that breast cancer death rates could be reduced by as much as 30 percent if all women followed the recommended mammography guidelines.

Use of mammography is higher among white women than among blacks and higher among women with higher incomes, women with more years of formal education and women who are married, according to the survey.

Women in their fifties are most likely to undergo regular mammograms as recommended. Compliance with the recommendations tends to decline with advancing age, and fewer than 20 percent of women in their seventies have an annual mammogram, the survey found.

Among women who had had only one mammogram in their lives, about one in three erroneously believed that since that first mammogram was negative, they did not need another.

Nearly 40 percent of the women said mammograms "cost too much," and half said they would not pay as much as $150 for an annual breast X-ray.

(A typical mammogram costs between $100 and $125, but they can range up to about $250.)

The findings point to a crucial role for doctors in persuading women to undergo regular breast cancer screening. Nearly three quarters of the women who had had a mammogram reported that they did so on the advice of a physician. Nearly half who had not said it was because no doctor ever told them to.