LONDON -- Joseph Rotblat, who was the only scientist to resign from the Manhattan Project and later received the Nobel Peace Prize for his efforts to rid the world of atomic weapons, has died at the age of 96, his spokesman said yesterday.
Mr. Rotblat and the Pugwash Conferences on Science and World Affairs, the group he founded to promote nuclear disarmament, received the prestigious prize in 1995.
Mr. Rotblat, who was born in Warsaw and became a British citizen in 1946, died peacefully in his sleep in London on Wednesday night, the group said.
''Joseph Rotblat was a towering figure in the search for peace in the world, who dedicated his life to trying to rid the world of nuclear weapons, and ultimately to rid the world of war itself," said M.S. Swaminathan, president of the Pugwash Conferences.
Mr. Rotblat's penchant for holding science accountable began early in his career, when he was a part of the Manhattan Project that was seeking to build an atomic bomb. He resigned from the project after it became clear that Germany was not developing its own nuclear weapon.
On July 9, 1955, Mr. Rotblat and 10 other scientists, including Albert Einstein, Bertrand Russell, Frederic Joliot-Curie, and 1962 Nobel peace laureate Linus Pauling, issued a manifesto in London declaring that researchers must take responsibility for their creations, such as the atomic bomb.
Later, in 1957, Mr. Rotblat helped to found the group in Pugwash, Nova Scotia. Pugwash takes its name from the Indian word ''pagwechk," which means ''shallow water."
In awarding the peace prize, the Nobel committee said it was honoring efforts by Mr. Rotblat and his group to ''diminish the part played by nuclear arms in international politics and in the longer run to eliminate such arms."
They have worked to get scientists to ''take responsibility for their inventions" out of a ''desire to see all nuclear arms destroyed and, ultimately, in a vision of other solutions to international disputes than war," the Nobel citation read.
In his Nobel lecture, Mr. Rotblat said the group's goal of a war-free world was ''not Utopian."
''There already exist in the world large regions, for example, the European Union, within which war is inconceivable. What is needed is to extend these to cover the world's major powers," he said.
The group's secretary-general, Paolo Cotta-Ramusino, said Mr. Rotblat ''possessed the extraordinary combination of scientific rigor and moral integrity that we believe is, and has been, the hallmark of the Pugwash Conferences on Science and World Affairs since 1957."
''Indeed, without Jo, there would have been no Pugwash, and far less pressure from the scientific community on governments to abandon nuclear weapons," he said.
Mr. Rotblat received a master's degree from the University of Poland in 1932 and a doctorate in physics from the University of Warsaw in 1938. He worked at a radiological laboratory in Warsaw from 1933-39 and as the assistant director of the Free University of Poland's Atomic Physics Institute.
He married Tola Gryn in 1937, but left his wife behind in Poland when he went to the University of Liverpool in 1939 because she was too ill to travel. She was later imprisoned by the Nazis in a concentration camp and did not survive.
After leaving the Manhattan Project, he returned to the University of Liverpool, working in the physics department. He joined the University of London in 1950 and worked there until 1976.
Mr. Rotblat's other honors included a knighthood in 1998, the Albert Einstein Peace Prize in 1992, the Copernicus Medal of the Polish Academy of Scientists in 1996, and the Jamnalal Bajaj Peace Award in 1999.
Mr. Rotblat, who never remarried, leaves two nieces, and several great-nieces and great-great nephews. Funeral plans were not announced.