His wife, Lisa Feiner, confirmed his death.

Dr. Commoner was a leader among a generation of scientist-activists who recognized the toxic consequences of America's post-World War II technology boom, and one of the first to stir the national debate over the public's right to comprehend the risks and make decisions about them.

Raised in Brooklyn during the Depression and trained as a biologist at Columbia and Harvard, he came armed with a combination of scientific expertise and leftist zeal. His work on the global effects of radioactive fallout, which included documenting concentrations of strontium 90 in the baby teeth of thousands of children, contributed materially to the adoption of the Nuclear Test Ban Treaty of 1963.

From there it was a natural progression to a range of environmental and social issues that kept him happily in the limelight as a speaker and an author through the 1960s and '70s, and led to a wobbly run for president in 1980.

In 1970, the year of the first Earth Day, Time magazine put Dr. Commoner on its cover and called him the Paul Revere of Ecology. He was by no means the only one sounding alarms — the movement was well under way by then, building on the impact of Rachel Carson's book "Silent Spring" in 1962 and the work of many others. But he was arguably the most peripatetic in his efforts to make environmentalism a people's political cause.

(The same issue of Time also noted that President Richard M. Nixon had already signed on. In his State of the Union address that January, he said: "The great question of the '70s is, shall we surrender to our surroundings, or shall we make our peace with nature and begin to make reparations for the damage we have done to our air, to our land and to our water?" And he followed through: Among other steps, the Environmental Protection Agency was established in December 1970.)

Dr. Commoner was an imposing professorial figure, with a strong face, heavy eyeglasses, black eyebrows and a thick head of hair that gradually turned pure white. He was much in demand as a speaker and a debater, especially on college campuses, where he helped supply a generation of activists with a framework that made the science of ecology accessible.

His four informal rules of ecology were catchy enough to print on a T-shirt and take to the street: Everything Is Connected to Everything Else. Everything Must Go Somewhere. Nature Knows Best. There Is No Such Thing as a Free Lunch.

Although the rules were plain enough, the thinking behind them required leaps of faith. Dr. Commoner's overarching concern was not ecology as such but rather a radical ideal of social justice in which everything was indeed connected to everything else. Like some other left-leaning dissenters of his time, he believed that environmental pollution, war, and racial and sexual inequality needed to be addressed as related issues of a central problem. Having been grounded, as an undergraduate, in Marxist theory, he saw his main target as capitalist "systems of production" in industry, agriculture, energy and transportation that emphasized profits and technological progress with little regard for consequences: greenhouse gases, nonbiodegradable materials and synthetic fertilizers and toxic wastes that leached into the water supply.

He insisted that the future of the planet depended on industry's learning not to make messes in the first place, rather than on trying to clean them up. It followed, by his logic, that scientists in the service of industry could not merely invent some new process or product and then wash their hands of moral responsibility for the side effects. He was a lifelong opponent of nuclear power because of its radioactive waste; he scorned the idea of pollution credit swaps because after all, he said, an industry would have to be fouling the environment in the first place to be rewarded by such a program.

In a "Last Word" interview with The New York Times in 2006, videotaped to accompany this obituary online, Dr. Commoner elaborated on his holistic views and lamented the inability of society to connect the dots among its multitude of challenges, "an unfortunate feature of political development in this country."

Noting the success of movements that had separately promoted civil rights, sexual equality, organized labor, environmentalism and an end to the war in Vietnam, he said one might think that "if they would only get together, they could remake the country."

Then he said: "I don't believe in environmentalism as the solution to anything. What I believe is that environmentalism illuminates the things that need to be done to solve all of the problems together. For example, if you're going to revise the productive system to make cars or anything else in such a way as to suit the environmental necessities, at the same time why not see to it that women earn as much as men for the same work?"

Dr. Commoner's diagnoses and prescriptions sometimes put him at odds with other environmental leaders. He is rightly remembered as an important figure in the first Earth Day (April 22, 1970), a nationwide teach-in conceived by Senator Gaylord Nelson of Wisconsin, and he himself regarded the observance as historically important. But Earth Day also illustrated the growing factionalization of a movement in which "environmentalism" could mean anything from ending the Vietnam War to growing one's own cabbages, and a number of singular, easily grasped agendas were competing for attention and money.

This was the context for the rift between Dr. Commoner and advocates of population control, who saw environmental degradation as a byproduct of overpopulation and who had become a force on the strength of Paul R. Ehrlich's huge best seller "The Population Bomb." Conservationist groups like the Sierra Club and the National Wildlife Federation were strong supporters of Dr. Ehrlich's views.

Dr. Commoner took aim at the "neo-Malthusians." On a scientific panel discussion with Dr. Ehrlich in December 1970, he said it was "a cop-out of the worst kind" to say that "none of our pollution problems can be solved without getting at population first."

He elaborated in his best-known book, "The Closing Circle," published the next year. Reducing population, he wrote, was "equivalent to attempting to save a leaking ship by lightening the load and forcing passengers overboard."

"One is constrained to ask if there isn't something radically wrong with the ship."

In the traditional science establishment, Dr. Commoner's standing was ambiguous. Along with eminent figures of the postwar years like the chemist Linus Pauling and the anthropologist Margaret Mead, he was concerned that the integrity of American science had been compromised — first by the government's emphasis on supporting physics at the expense of other fields during the development of nuclear weapons, and second by the growing privatization of research, in which pure science took a back seat to projects that held short-range promise of marketable technologies.

It was a concern remarkably similar to that of the distinctly unradical Dwight D. Eisenhower, who warned of the dangerous power of "the military-industrial complex" as he was leaving the presidency. But although Dr. Commoner had a record of achievement as a cellular biologist and founding director of the government-financed Center for the Biology of Natural Systems , he was seen primarily as the advocate for a politics that relatively few considered practicable or even desirable. Among other positions, he advocated forgiveness of all third-world debt, which he said would decrease poverty and despair and thus act as a natural curb on population growth.

His platform did not get him very far in the 1980 presidential race, which he entered as the head of his own Citizens' Party. He won only 234,000 votes as Ronald Reagan swept to victory. Dr. Commoner himself conceded that he would not have made a very good president. Still, he was angry that the questions he had raised had generated so little interest.

His own favorite moment of the campaign, he recalled many years later, was when a reporter in Albuquerque asked, "Dr. Commoner, are you a serious candidate, or are you just running on the issues?"

Barry Commoner was born on May 28, 1917, in the East New York neighborhood of Brooklyn. His parents, the former Goldie Yarmolinsky and Isidore Commoner, were Jewish immigrants from Russia, his father a tailor until he went blind. (The original family name, Comenar, was Anglicized at the suggestion of an uncle of Barry's, Avrahm Yarmolinsky, chief of the Slavonic department at the New York Public Library.)

Young Barry grew up at a time when it was possible to be both a tough street kid and a studious sort. He spent hours in Prospect Park collecting bits of nature, which he took home to inspect under a microscope that Uncle Avrahm had given him.

He was so shy at James Madison High School that he was referred to a speech correction class, and after graduation he set out on the track of a quiet academic career. With money earned from odd jobs, he put himself through Columbia, earning honors in his major, zoology; election to Phi Beta Kappa and Sigma Xi; and a B.A. degree in 1937, at 20. He went on to do graduate work at Harvard, where he got a Ph.D. in cellular biology. He taught for two years at Queens College and served in the Naval Air Corps in World War II, rising to lieutenant. In 1947 he joined the faculty of Washington University in St. Louis.

Parallel to his life as a public figure, Dr. Commoner had a reputation as a brilliant teacher and a painstaking researcher into viruses, cell metabolism and the effects of radiation on living tissue. A research team he led was the first to show that abnormal free radicals — groups of molecules with unpaired electrons — might be the earliest indicator of cancer in laboratory rats.

He found his political voice when he encountered the indifference of government authorities to the high levels of strontium 90 in the atmosphere from atomic tests. Quite simply, he said in an interview with The Chicago Tribune in 1993, "The Atomic Energy Commission turned me into an environmentalist."

He helped to organize the St. Louis Committee for Nuclear Information in 1958, and eventually served as its president. Dr. Commoner told Scientific American years later that the committee's task "was to explain to the public — first in St. Louis and then nationally — how splitting a few pounds of atoms could turn something as mild as milk into a devastating global poison."

"At about that time," he continued, "several of us met with Linus Pauling in St. Louis and together drafted the petition, eventually signed by thousands of scientists worldwide." The petition was part of the scientific underpinning for President John F. Kennedy's proposal of the Nuclear Test Ban Treaty of 1963 — "the first of continuing international actions to fully cage the nuclear beast," Dr. Commoner said

As the founding director of the Center for the Biology of Natural Systems in St. Louis, he led a staff drawn from many disciplines in investigating, among other things, lead poisoning in slums, the ecology of ghetto rats, the economics of conventional versus organic farming, and the pollution of rivers by fertilizer leaching.

Dr. Commoner moved the center from St. Louis to Queens College in 1981. He remained in the thick of things, helping to set up New York City's trash recycling program and defending it against critics like Mayor Rudolph W. Giuliani, who had declared the recycling law irresponsible.

In 2000, at 82, Dr. Commoner gave up the directorship of the center to concentrate on new research projects, including work on the effects of genetically altering organisms.

By then he was no longer getting anything like the attention he had enjoyed in earlier times. Some experts had begun to think that his view of the planet, as a place harmoniously balanced by the trial and error of long evolution, left out too much complexity and too much potential for the unexpected.

Stephen Jay Gould, the Harvard paleontologist and evolutionary biologist, reviewing Dr. Commoner's 1990 book "Making Peace With the Planet" for The Times in 1990, said that it "suffers the commonest of unkind fates: to be so self-evidently true and just that we pass it by as a twice-told tale."

"Although he has been branded by many as a maverick," Dr. Gould added, "I regard him as right and compassionate on nearly every major issue."

Dr. Commoner married Ms. Feiner in 1980. He is also survived by two children, Lucy Commoner and Frederic, by his first wife, the former Gloria Gordon; and one granddaughter.

Dr. Commoner practiced what he preached. In his personal habits he was as frugal as a Yankee farmer, and as common-sensical. He drove cars or took taxis if the route by public transit took him far out of his way. On the other hand, he saw no need to waste electricity by ironing his shirts.

And when a Times writer once asked his Queens College office to mail some material, it arrived in an old brown envelope with the crossed-out return address of the botany department at Washington University — a place where he had last worked 19 years earlier.