"It was like an atomic mushroom cloud," said policeman Aaturnino Ramos, describing how an explosion and 150-foot-high, gasoline-fed flames that followed it reduced the coastal shantytown of Vila Soco to ashes, leaving at least 90 charred and unrecognizable bodies.

Indeed, the devastated landscape of splintered habitations and oily mud, onto which rescue workers scattered quicklime to dissolve unfound fragments of bodies, bore an uncanny resemblance to photos of Hiroshima.

But the explosion on the night of Feb. 24 that destroyed the shantytown in the grimy industrial municipality of Cubatao on Brazil's southern coast was caused not by war, but by 175,000 gallons of gasoline that leaked from an underground pipeline. Before igniting, the fuel spread across a marshy area where at least 600 families lived.

In a separate incident, to the north in Brazil's Amazonian region, experts were examining traces of destruction in an investigation that recalls another kind of warfare--that practiced in Vietnam. So-far-unsubstantiated charges have been made that at least 13 people died and dozens of cattle perished after a government subcontractor working on electric power lines in 1982 illegally used the chemical Agent Orange, a military defoliant.

These are just the latest in a series of industrial accidents that support the conferring of the title of the world's worst polluter on Brazil by a 1982 United Nations environment conference held in Nairobi.

Incidents such as these also raise fears that Brazil's headlong rush for industrial modernization is being achieved at the cost of basic safeguards.

In the Vila Soco case, state-owned Petrobras, which operated the pipeline and is the world's 10th-largest oil company outside the United States, admitted that errors by those operating valves at the refinery terminal forced a burst in the 25-year-old piping.

Company President Shigeaki Ueki agreed to pay compensation to the 600 families made homeless, and made some out-of-court settlements with relatives of those who died. But he blamed state authorities for ignoring his repeated warnings about the dangers of allowing slum dwellers to build on top of the pipeline, and he disputed a $13,000 fine imposed by Sao Paulo state environmental protection authorities.

Sao Paulo chief attorney Paulo Salvador Frontini said those responsible for the 90 deaths and 35 serious injuries would face trial on criminal incendiary charges.

Since Brazilian delegates told a 1972 U.N. environment conference in Stockholm that "poverty is the worst pollution" and that nothing would be done to check the pace of Brazil's industrial progress, spots such as Cubatao have spread across southern Brazil.

The town's reputation as the world's dirtiest city has earned it the title "valley of death," and its 80,000 residents are exposed to serious health risks.

A project funded by the National Scientific Research Council found that 12 in every 10,000 babies were born without brains--three times the national average.

A study by Sao Paulo University's Department of Medicine found that 44 percent of those examined suffered lung diseases caused by tons of waste scattered into the atmosphere by the town's 23 heavy industrial plants. Eighty-one percent of those examined also showed red-blood-cell deficiencies.

Thousands of industrial workers live in shantytowns similar to Vila Soco, but perched on steep hillsides in constant danger of landslides.

Such dangers exist elsewhere; last year 99 people died when a train carrying gasoline was derailed and exploded hours later in the center of Pojuca, a town in Bahia state. As in the case of Vila Soco, authorities did little to stop residents from collecting spilt fuel in tins to sell.

The Cubatao leakage is hardly the first from Petrobras installations, many of them dating back to the 1940s. Since 1980 the company has been fined 20 times for oil spills by Sao Paulo state's environmental watchdog, Cetesb.

"We are at the same stage as the U.S. in the 1960s," said Carlos Celso do Amaral e Silva, a Cetesb senior adviser, who nevertheless believes Brazil's environmental laws have improved considerably in the last decade. "The laws are wonderful, but they just don't work. The problem is enforcement," he said in an interview.

Cetesb fined Petrobras last October after 1,500 tons of crude oil leaking from a pipeline caused major environmental damage in the Bertioga coastal region.

But Celso said most spillages occur at the Sao Sebastian terminal close by, where tankers unload much of the 600,000 barrels of oil Brazil imports daily.

Brazil is not a signatory to the U.N. Treaty on Maritime Trade, so many operators of bulk tankers that bring in oil and ship out iron ore on the return trip have no qualms about washing waste oil from holds inside territorial waters.

Until now Brazil's thinly stretched navy has been unable to police the tankers, while Cetesb's modest facilities are the only means available for cleaning up spills.

"When a disaster occurs, public attention is focused on the matter and things change," said Celso. He said Petrobras was backing up its new-found concern by installing an oil-spillage and tank-cleaning unit, with U.N. aid, at the oil terminal.

At the federal level, the only organ with muscle to act against polluters--many of them state-owned companies with powerful connections in the military-backed government--is the special secretariat for the environment, Sema.

Sema acted following allegations by a committee of inquiry last December that Agromax, a firm subcontracted by the government utility Eletronorte, had used Agent Orange chemical defoliant to clear trees around power lines at Tailandia in the Amazon state of Para.

After Agromax used herbicides to stop scrub resprouting under high-tension power lines running from the hydroelectric power dam at Tucurui, authorities received reports of at least 13 deaths and 12 unexplained miscarriages in rural communities near the line. Dozens of cattle also died.

Sema fined Agromax for careless use of Tordon 101 and Tordon 155 herbicides, manufactured by Dow Chemical Corp. and sold here by its subsidiary. Contractors were alleged to have handed out herbicide to local farmers, and washed their protective clothing in waterholes used by cattle.

"I saw men washing the masks and gloves they used for applying the poison. One day my 13-year-old daughter went to wash her clothes at the same waterhole and got sick. We took her to a hospital but she died the next day," Epitacio Gomes da Silva told officials.

Although the active ingredients of the two Tordon formulas used separately at Tailandia are poisons known as 2,4,5t and 2,4d, which were used in Agent Orange defoliant deployed by U.S. forces in Vietnam, Dow Chemical strongly denies that the chemicals, which have been on sale for years, are unsafe. Dow also says they do not produce any harmful effects.

Dow said Agent Orange was made only for the U.S. Defense Department in the 1960s, and was never sold elsewhere. It said that, although both Tordon formulas were used, Agent Orange is not produced by mixing them.

A Dow spokesman in Sao Paulo, David Tingerfelt, said that no suits have been brought because of the deaths. He pointed out that four independent Brazilian scientific studies had blamed the mysterious deaths on tropical diseases and malnutrition. The cattle were said to have died from parasite and mineral deficiency.

But Para's state government is energetically pursuing the allegations and has exhumed bodies of those who died in 1982 for expert examination in Sweden.

"Certainly they won't find any Tordon--it's biodegradable," said Lingerfelt. "Dow's position is clear and tranquil: There's no scientific proof of any connection between the Tordon application and the allegations--our herbicides don't have that effect."

Allegations that illegal defoliants have been used in the Amazon are not new. A veteran researcher for the government statistics institute Ibge, Orlando Vilaverde, told reporters that Agent Orange was employed in the 1970s by big landowners using planes to oust squatters and Indians from areas where they held land titles in the remote jungle state of Acre.

A senior official at Eletronorte, who requested his name not be used, also confirmed a decision to scrap plans to use chemical defoliants to clear the forest area destined to be drowned as the reservoir for the giant $5 billion Tucurui hydroelectric dam on an Amazon tributary.

In 1982 the Amazon Research Institute Inpsa decided defoliants would be used to clear millions of tons of leaves from the Tucurui Basin to avoid acidity problems in the reservoir, but desisted after Paulo Nogueira Neto, the head of the federal environmental watchdog agency, Sema, warned that it would violate the Amazon Pact and threatened to resign over the issue.

"Eletronorte has never used Agent Orange and will not use any chemicals in the Tucurui Basin," said the utility official.