ITHACA, N.Y. -- James A. Krumhansl, a professor of physics emeritus at Cornell University who led the scientific community's opposition to the superconducting supercollider in the 1980s, died May 6 in Hanover, N.H. He was 84.

It was while Krumhansl was president-elect of the American Physical Society (APS) in 1987 that he testified before Congress that the supercollider should not be built if the cost would penalize superconductivity research funding. Although Krumhansl, who became president of the APS in 1989, was not speaking for the society, his words carried great weight with Congress, which in 1993 halted the project after14 miles of tunneling were completed and two billion dollars spent.

Krumhansl's research focused on theoretical condensed matter physics and materials science, but his research interests also included communication and information systems, applied mathematics, nonlinear science and molecular biological physics. He was particularly known for his work on phonons (quantized sound), solitons (particle-like waves) and defects in materials,

His 50-year career at Cornell began with graduate studies in 1940 and continued until his retirement as the Horace M. White Professor in 1990.

Krumhansl received his B.S. in electrical engineering from the University of Dayton in 1939 and his M.S. in physics from Case Western Reserve University in 1940 (from which he also received an honorary doctorate in 1980). He was awarded his Ph.D. by Cornell in 1943.

During World War II, he worked for the U.S. Navy at Stromberg-Carlson on microwave pulse communication systems and secrecy systems, receiving patents on pulse coding communications circuits. He was associate director of research for Union Carbide in the 1950s, and from 1960 to 1964 he was director of Cornell's Laboratory of Atomic and Solid State Physics.

Krumhansl cofounded the Materials Research Council at the Defense Advanced Research Projects Agency at the U.S. Department of Defense. From 1977 to 1979, he was assistant director for mathematics, physical science and engineering at the National Science Foundation, where he led program development in microscience and computer systems. He also was a consultant to the director of the Los Alamos National Laboratory.

He served on the board of the American Institute of Physics and was editor in chief of Physical Review Letters and the Journal of Applied Physics .

He was a Guggenheim fellow, a National Science Foundation senior postdoctoral fellow at the University of Oxford, a Fulbright fellow to Yugoslavia, a Royal Society visiting fellow at the University of Cambridge and a visiting fellow at Cambridge and Oxford.

After retiring from Cornell he lived in Amherst, Mass., and Hanover. He is survived by two sons, James and Peter; a daughter, Carol; a grandson, Robert, and a granddaughter, Kira.