ictor F. Weisskopf, a nuclear physicist who worked on the Manhattan Project to build the first atomic bomb in World War II and later became an ardent advocate of arms control, died on Monday at his home in Newton, Mass. He was 93.

Dr. Weisskopf was one of the first physicists to warn of the possible dangers of atomic research. In 1939, he and Leo Szilard, another atomic physicist, recommended that physicists keep secret their findings on nuclear fission instead of publishing them in academic journals, out of fear that the information could help Nazi scientists build atomic weapons.

In 1943, Dr. Weisskopf joined the Manhattan Project as associate head of the theory division. In a lecture at the Massachusetts Institute of Technology in 1991, he recounted the rationale for dropping the bomb on Hiroshima in August 1945, that the destruction needed to have a strong psychological effect on Japan.

The second bomb, dropped on Nagasaki three days later, was more troubling to him.

"The second bomb I don't hesitate to call a crime," Dr. Weisskopf told the audience at M.I.T. He also called the cold war "a collective mental disease of mankind."

Early in his career, Dr. Weisskopf laid the groundwork for fixing a fundamental flaw in applying quantum mechanics to electromagnetism. After World War II, he furthered understanding of how the nuclei of atoms behave.

"He really made so many contributions that it's hard to identify any single one," said Dr. Robert L. Jaffe, director of the Center for Theoretical Physics at M.I.T.

Dr. Weisskopf also lent his name and voice to political issues. In letters and opinion pieces in newspapers, he repeatedly warned of the dangers of nuclear war. Although he was of Jewish descent, he was appointed by Pope Paul VI to the 70-member Pontifical Academy of Sciences in 1975, and in 1981 he led a team of four scientists sent by Pope John Paul II to talk to President Ronald Reagan about the need to prohibit the use of nuclear weapons.

Victor Frederick Weisskopf was born Sept. 19, 1908, in Vienna. He earned his doctorate in physics at the University of Göttingen in Germany in 1931.

In postdoctoral studies at the University of Berlin, University of Copenhagen, Cambridge University and the Institute of Technology in Zurich, Dr. Weisskopf apprenticed with many great founding physicists of quantum mechanics: Werner Heisenberg, Erwin Schrödinger, Niels Bohr and Wolfgang Pauli.

In 1937, shortly before Germany absorbed Austria, Dr. Weisskopf immigrated to the United States, landing a position at the University of Rochester.

After the war, he became a professor at M.I.T. From 1961 to 1965, he served as director-general of the CERN particle accelerator in Switzerland before returning to M.I.T. He retired in 1974.

In the 1930's, he and Pauli wrote a paper applying quantum mechanics to "spinless" particles, which they regarded as a mathematical obscurity, because at that time all known particles like protons, electrons and neutrons carried spin, or angular momentum, like a spinning top. Only a few years later, such spinless particles appeared in the high-energy collisions at particle accelerators.

In the 1930's, Dr. Weisskopf tackled the application of quantum mechanics to electromagnetic fields. At the time, physicists' calculations were producing absurd answers: electrons were infinitely massive and produced infinitely powerful electric fields.

Dr. Weisskopf was among the first scientists to suggest a mathematical technique to rein in the unruly equations, essentially imagining that an infinitely large charge would induce a cloud of "virtual particles" fluttering in and out of existence around it that would nearly offset infinite charge.

"He was the first person to make significant progress in taming the infinities of field theory," Dr. Jaffe said.

A decade later, the theory was completed by three physicists, Sin-Itiro Tomonaga, Julian Schwinger and Richard Feynman. It won them a Nobel Prize in 1965.

"He had done work at the frontiers of theoretical physics in the 1930's that perhaps was only partly successful because it was so far ahead of its time," said Dr. Steven Weinberg, a professor of physics at the University of Texas.

Dr. Weisskopf was a member of the National Academy of Sciences. He was president of the American Physical Society in 1960-61 and president of the American Academy of Arts and Sciences from 1976 to 1979.

His 1952 textbook, "Theoretical Nuclear Physics," written with John M. Blatt, was the basic reference for the new field. He also wrote essays for a public audience, including his memoir, "The Joy of Insight: Passions of Physicist" (Basic Books, 1991).

His honors included the Medal of Science, the Wolf Prize in Physics and the Enrico Fermi Award.

His first wife, Ellen, died in 1989.

He is survived by his second wife, Duscha; a son, Thomas E., of Ann Arbor, Mich.; a daughter, Karen Worth of Newton; and five grandchildren.

In the often competitive field of theoretical physics, Dr. Weisskopf stood out as unusually generous and modest. Dr. Jaffe recalled how in the mid-1970's, when he was a new faculty member at M.I.T., he and his collaborators would talk to Dr. Weisskopf about the theory they were developing to describing the behavior of quarks, the constituent particles of protons and neutrons.

Dr. Jaffe said Dr. Weisskopf did not understand all the complexities in the theory, but "he listened patiently" and provided a crucial insight that helped them solve the problem. The researchers added Dr. Weisskopf as an author to acknowledge his contribution.

"He tried to get us to take it off the paper," Dr. Jaffe said. "He said, `The only thing I contributed to this paper was the `don't-know-how.' "

Dr. Weisskopf's name remained on the paper.