Robert C. Cook, 92, a demographer, geneticist and author who was among the first to warn of the dangers of human overpopulation, died of pneumonia Jan. 7 at Collington Retirement Community in Mitchellville.

Mr. Cook was editor of the American Genetic Association's Journal of Heredity from 1922 until 1962, and in that capacity began to publish articles during the 1930s advocating birth control and warning that disastrous consequences would result from runaway population growth.

He was president of the Population Reference Bureau, a private nonprofit organization that collected and distributed information on population issues, from 1959 to 1968, and while serving there was a frequent witness before congressional committees on matters related to overpopulation.

His major work on the subject, "Human Fertility: The Modern Dilemma," was published in 1951. "Next to the atom bomb, the most ominous force in the world today is uncontrolled fertility," Mr. Cook argued in the book.

He declared that "rampant fecundity has produced more hungry mouths than can be fed. The scramble for bare subsistence by hordes of hungry people is tearing the fertile earth from hillsides, destroying forests and plunging millions of human beings into utter misery."

Improvements in modern medicine and public health measures, Mr. Cook noted, had brought about a substantial reduction in the death rate, while birth rates were holding at traditional levels, thus creating a rapid and ominous rise in worldwide population.

A native Washingtonian, Mr. Cook was the son of the noted botanist, Orator Fuller Cook, who believed his children could be best educated outside of the traditional school system. The younger Cook attended Sidwell Friends School for one year when he was 13, and had one year of premedical study at George Washington University, but then left during World War I to design airfoils at the National Bureau of Standards.

He became editor of the Journal of Heredity at the urging of Alexander Graham Bell and others, and during his early years there also served as executive officer of the American Genetic Association. In this role he worked with several authors, including Julian Huxley, and helped shape the relatively young science of genetics.

Mr. Cook's warnings during the 1930s about the dangers of the explosive growth of the world population came at a time when many demographers were forecasting a downward trend in population growth. He was author in 1939 of one of the first major articles to be published in a popular magazine, Collier's, on the subject of overpopulation, "Bootleg Birth Control," in which he advocated contraception "as a means to population balance."

In that article Mr. Cook also advocated eugenics, calling for more births among the "groups of higher intelligence and better economic backgrounds," and fewer from the "least intelligent, least trained and least capable groups," a concept that fell into disfavor after the brutal excesses of the Nazis in Germany.

His warnings on population growth began to receive wide attention during the 1950s and 1960s. In 1955 he was co-recipient of the Albert and Mary Lasker Foundation's planned parenthood award for his "outstanding contribution to wider understanding of the world population problem."

After retiring from the Population Reference Bureau in 1968, Mr. Cook continued to write and serve as a private consultant.

He was a former lecturer in genetics at George Washington University Medical School and a member of the Population Association of America.

He also was a member of the Cosmos Club, and had donated a copy of "Human Fertility" to the club library with the inscription, "To the members of the Cosmos Club, to whom fertility has ceased to be a dilemma and has become an abstraction."

His marriage to the former Margaret Brown ended in divorce.

Survivors include his wife of 44 years, Annabelle Desmond Cook of Mitchellville; a daughter of his first marriage, Victoria Sprenger of Charleston, W.Va.; seven grandchildren; and nine great-grandchildren.