Dr. Rees was born in Cleveland. She went to school in New York, attended Hunter College High School and graduated summa cum laude from Hunter College in 1923. She completed graduate studies at Columbia University, where she also studied law. She received a Ph.D. in mathematics from the University of Chicago in 1931.
In the meantime, in 1926, she returned to Hunter as a mathematics instructor. Dr. Rees was an associate professor during World War II, when she went to work for the Government, helping to direct research in modern mathematics for the war effort.
Dr. Rees was trained in pure algebra, but she was gifted with common sense and a knack for the practical, which stood her in good stead in dealing with the military.
''I could sass the admirals as the men couldn't,'' she recalled later.
She was sent to the applied mathematics panel of the National Defense Research Committee in the Office of Research and Development.
By 1946, she was head of the mathematics branch of the Office of Naval Research, a position that she held until 1949, after which she was deputy director of the entire science division until 1953.
She worked on projects like fluid flow to solve antisubmarine problems, hydrofoil designs and early rocketry. She was awarded the President's Certificate of Merit and the British Medal for Service in the Defense of Freedom.
Dr. Rees also had an important role in the growth and diversification of mathematical studies. Many of her ideas left their mark on fast computer technology.
Dr. Rees returned to Hunter in 1953, as a professor and dean of students. She was responsible for academic affairs, including curriculum development, admissions standards, faculty recruitment and budgeting for teaching and research.
She became the first dean of graduate studies at CUNY in 1961, when the university drew up its doctoral programs. She was named president of the graduate division in 1969 and president of the newly consolidated Graduate School and University Center on 42d Street in 1971, before retiring the next year.
Dr. Rees was a Presidential appointee to the board of the National Science Foundation from 1964 to 1970, and she was active in the American Mathematical Society and the Mathematical Association of America, among other groups.
Dr. Rees enjoyed a crowning moment in 1969, when the 120,000-member American Association for the Advancement of Science elected her president. Women remained something of a rarity at that level in the scientific community, but she -- as Marie Curie, Lisa Meitner and Dr. Margaret Mead before her -- had proved that scientific creativity was not just for men.
Dr. Rees's husband, Dr. Leopold Brahdy, died in 1977.
By WOLFGANG SAXON, October 28, 1997 © The New York Times Company