The government's top health scorekeeper said yesterday that "the most startling, most important" rise in cancer deaths in the last quarter century occured among black and other nonwhite adult males.

Dorothy R. Rice, director of the National Center for Health Statistics, said that between 1950 and 1975 the increase in the cancer death rate per 100,000 population was more than twice as high for nonwhite adult males than it was for white adult males.

Specifically, deaths among nonwhite adult males in the 25-ear period totaled 288,436. Had the 1950 morwhite adult males in the 25-year period totaled 288,436. Had te 1950 mortality rate held steady, 74,049 of them - 26 per cent - would not have died of cancer.

During the same period, deaths among adult white males totaled 2,379,860. had their 1950 mortality rate held steady, 284,907 - 12 per cent - would not have died of cancer.

Why the difference? Rep. L. H. Fountain (D-N.C.) asked at the first congressional hearing into the National Cancer Institute's management of "the war on cancer."

Rice said at least part of the answer lay in the heavy mogration of blacks from rural reas into industrialized cities where, in higher proportions than whites, they took jobs that exposed them to cancer-causing chemicals.

Cancer deaths per 100,000 population have risen almost without interruption - from 100.6 in 1930, when the government first gathered reliable statistics, to 171.7 in 1975.

An aging population - age heightens vulnerability to cancer - accounted for much of the increase in the mortality rate, Rice told Fountain, chairman of the House Intergovernmental Relations and Human Resources Subcommittee.

But that doesn't explain 19 per cent of the increase, she told Fountain. And 19 per cent, she said, figures out to 47,600 deaths in 1975 alone.

After adjustment for age, cancer mortality in females declined 10 per cent between 1950 and 1975. During the same period, the age-adjusted cancer death rate for men rose 23 per cent.

In males, her data show, fatal cancer at most body sites increased at a relatively modest pace. But fatal lung cancer in men skyrocketed - from 17 per 100,000 in 1950 to 67 per 100,000 in 1975.

"Men began to smoke earlier than women did," Rice said. Men may have had more occuptional exposure to carcinogens."

Rep. John W. Wydler (R-N.Y.) pointed to a discomfiting fact in Rice's charts: the number of cancer deaths accounted for neither by aging of the population nor by its growth has risen disproportionately in the period of greatest government spending for the National Cancer Program - "the war on cancer."

Can we expect "a dramatic increase" in the death rate? Wydler asked.

"It might well happen," said Rice, who said provisional data for 1976 showed increases of 2.5 per cent in the number of cancer deaths (to 375,000), of 1.7 per cent in the mortality rate unadjusted for age, and of 0.6 per cent in the age-adjusted death rate.

Fountain said that despite huge appropriations for the program since it began in 1971 (the current outlay is $815 million), the cure rate of 1 in 3 has not changed since 1957.

Leading scientist who testified agreed that there were troubles in the management of the program. But they differed over whether the program is a success - or will be proved later to be one - or a failure.

Dr. Irwin D. J. Bross chief of Health statistics for Roswell Park Memorial Institute, a leading cancer research center in Buffalo, N.Y., charged that the program has been so mismanaged it is producing more cancer than it is preventing.