For the first time since the 1930s, the number of new cancer cases in the United States is declining, federal officials said on Thursday in announcing a sharp reversal in the incidence of diseases that kill more than 1,500 Americans each day.

Deaths from cancer are also dropping, continuing a trend that was first reported in November 1996. Together, the two developments offer experts new hope that 27 years after President Richard Nixon declared "war on cancer," the nation may have reached a turning point."The burden of fear the public has been feeling should begin to lift," said Dr. James Marks of the Centers for Disease Control and Prevention said in releasing a national report card on cancer at a news conference here. "Cancer is conquerable and progress is being made."

Experts attribute the decline in new cases to changes in behavior, most notably a drop in smoking, and the decline in deaths to increased screening and better therapies. But the positive trends are not benefiting all Americans; minorities and women remain particularly at risk.

From 1990 to 1995, the study found, cancer rates for men and women of every race dropped, with one notable exception: black men. They have the highest cancer rates of any group in the nation, mainly because of a sharp rise in new cases of prostate cancer.

In the same period, new cases of breast cancer increased for black women. And new cases of lung cancer, while dropping sharply among men, rose among women who were white, Asian and Pacific Islander.

Marks said minorities are "less likely to be screened, less likely to have cancer detected."

The incidence of cancer in the United States has been rising since the 1930s, although the government has been keeping detailed annual statistics only since 1973. The rate of all new cancers combined dropped an average of 0.7 percent per year from 1990 to 1995, according to Thursday's report, which was jointly released by the disease control centers in Atlanta, the National Cancer Institute in Bethesda, Md., and the American Cancer Society in New York.