Jeremy J. Stone. (Federation of American Scientists/Federation of American Scientists)

Jeremy J. Stone, a persistent and outspoken activist on such issues as arms control, human rights and international scientific cooperation, whose ideas helped form the framework of the U.S.-Soviet Anti-Ballistic Missile Treaty of 1972, died Jan. 1 at his home in Carlsbad, Calif. He was 81.

A friend, Mark McCarty, said Dr. Stone had prostate cancer, but the cause of death was undetermined.

Dr. Stone, a son of crusading independent journalist I.F. Stone, began his career as a mathematician before turning to a life of activism in the 1960s. He later served 30 years as president of the Washington-based Federation of American Scientists, bridging a gap between science and politics.

Beginning in his 20s, Dr. Stone published a series of papers and books on nuclear disarmament. His most influential idea was the suggestion that restrictions on defensive antimissile systems could halt the nuclear arms race between the United States and the Soviet Union.

He argued that, by strengthening their antimissile defenses, the two superpowers would be locked in a never-ending struggle to build more powerful offensive weapons. If they were deployed, the inevitable result would be nuclear annihilation.

As the idea gained currency among U.S. arms control experts throughout the 1960s, Dr. Stone made repeated trips to Moscow to introduce the concept to Soviet scientists and officials.

In modified form, his notion became a key part of the Anti-Ballistic Missile Treaty, which was signed “probably in part because of his freelance diplomacy,” historian Metta Spencer wrote in the 2011 book “The Russian Quest for Freedom and Democracy.”

The treaty served as a brake on nuclear proliferation throughout the Cold War. In the wake of the attacks of Sept. 11, 2001, the administration of President George W. Bush announced it would withdraw from the treaty in 2002.

By then, Dr. Stone had a long record of speaking out on many issues affecting science and public policy. In the early 1970s, he questioned research and spending practices at the Pentagon, earning a spot on the so-called enemies list of President Richard M. Nixon.

He became a leading advocate on behalf of dissident Soviet scientist Andrei Sakharov, the winner of the 1975 Nobel Peace Prize. Dr. Stone traveled several times to the Soviet Union to meet Sakharov, who was held for years in internal exile. During the visits, Dr. Stone would smuggle in personal items, including razors, toiletries and a handheld computer.

In 1972, Dr. Stone led a delegation of U.S. scientists to China, soon after relations between the two countries were reopened. He later helped coordinate scientific exchanges with Iran and North Korea.

During the 1980s, he helped lead opposition to the proposed “star wars” missile defense program of President Ronald Reagan, noting that it would be a violation of the 1972 ABM Treaty.

Dr. Stone described the Federation of American Scientists, which he led from 1970 to 2000, as an “idea factory,” but the ideas were almost always his own, and in the beginning he was the factory’s sole worker.

The organization was formed by scientists from the Manhattan Project — the Allies’ atomic bomb program during World War II — concerned about the ethical use of science. By the time Dr. Stone took the helm, the federation had become dormant. He was its first full-time employee in more than 20 years. The annual budget was a minuscule $7,000.

He quickly revived the federation and built it into one of the country’s most visible platforms for presenting science-related topics as questions of urgent social concern.

“If Dr. Stone had not become the head of FAS in 1970, I believe that FAS would not exist today,” current federation president Charles D. Ferguson wrote in an email. “He took the helm when there was very little money left and a tiny membership base. Through a lot of hard work with a small, but dedicated team, Jeremy saved FAS by traveling across the United States to bring in thousands of scientists and other supporters and by establishing a headquarters in Washington.”

As many as 57 Nobel laureates signed on as public supporters of FAS. Dr. Stone appeared before congressional committees and wrote op-ed essays for newspapers.

Borrowing a tactic from his father, he published in-depth monthly newsletters. He delved into wide-ranging scientific topics, then wrote pointed editorials, doing virtually all the work single-handedly.

“I think Jeremy inherited from his father the idea that one person could make a difference,” John E. Pike, a space and nuclear expert who worked at FAS for 17 years, said in an interview. “Because he was not tied down by a large institutional apparatus, he had the luxury of doing what interested him at the time. It was the archetypal exemplar of an enterprise punching above its weight.”

Jeremy Judah Stone was born Nov. 23, 1935, in New York City. His father worked at several newspapers before launching I.F. Stone’s Weekly in 1953. He was often a lonely voice speaking out against McCarthyism, racial injustice and the Vietnam War.

Jeremy Stone graduated from Pennsylvania’s Swarthmore College in 1957 and received a doctorate in mathematics from Stanford University in 1960.

He was a research mathematician before working on arms control issues, first at the Hudson Institute in New York and later at Harvard University. He taught at Pomona College in Claremont, Calif., from 1966 to 1968, but he found himself increasingly drawn toward advocacy.

In 1971, I.F. Stone retired and asked his son to take over his muckraking weekly newsletter. Dr. Stone turned him down.

“I strongly preferred to create my own identity,” he wrote in a 1999 autobiography, “Every Man Should Try: Adventures of a Public Interest Activist.”

In that book, Dr. Stone suggested, on flimsy evidence, that a renowned Manhattan Project scientist, Philip Morrison, had been a Soviet spy. Morrison, who was still alive at the time, refuted the charge, which left Dr. Stone’s reputation indelibly stained.

He resigned from FAS in 2000. He later moved to California, where he launched an organization called Catalytic Diplomacy, which was engaged in a number of activities, including conflict resolution and dietary studies. He contributed to a 2016 documentary about his father and investigative journalism, “All Governments Lie.

Dr. Stone’s wife of 58 years, the former Betty Jane “B.J.” Yannet, died in 2015. Survivors include a brother and a sister.

For years, the Federation of American Scientists was housed in a townhouse on Capitol Hill that became a gathering place of the scientific and political elite.

“He ran in a very select crowd — Bill Colby, the former director of the CIA, Carl Sagan, you name it, they were there,” Pike recalled. “He created an environment in which you could rub shoulders with the great and the good.”