A nationwide campaign to discourage women from smoking is being undertaken by the American Medical Women's Association. The campaign will be the first concerted effort by female physicians to tackle smoking as a problem of particular concern to women, according to officers of the 10,000-member organization.

Last year, lung cancer overtook breast cancer as the leading cancer killer of women, and the trend is expected to continue this year. The American Cancer Society estimates that by the end of 1986, 41,100 women will die of lung cancer and 39,900 of breast cancer. Lung cancer remains the leading cancer killer among men, with 87,000 deaths in 1985 and a projected 89,000 in 1986, according to the cancer society.

Smoking is linked to many chronic conditions and diseases besides lung cancer, among them heart attacks, cardiovascular disease, strokes, emphysema and--of particular interest to women--problems related to pregnancy and childbirth. Smoking by women during pregnancy has been linked to lower birth weight and an increase in the risk of miscarriage, premature delivery and neonatal death.