Fishermen here say some days they get lost a few miles out to sea because giant clouds of petrochemical smoke blot out the shoreline.

Mayor Pompeyo Figueroa wants to prepare a civil defense and evacuation plan in case nearby jungles of tubes and tanks blow up or spring an uncontrollable leak of poisonous gas.

The editor of the local newspaper warns visitors not to try the seafood, saying most is contaminated by chemical waste and residents in the know eat only what is trucked from elsewhere on the Gulf of Mexico.

The oil boom has come and gone in this steamy port, leaving behind the country's largest petrochemical complex, a damaged environment and the promise of lean times to come under foul-smelling smoke. Environmental consequences of the boom might have been more palatable if the sharp rise in economic benefits had continued. But the collapse of oil prices has reversed that trend.

The effects of a new economic atmosphere are being felt throughout Mexico as President Miguel de la Madrid's government struggles with a $98 billion foreign debt and falling oil income. But perhaps nowhere has the bust become more starkly evident than in Coatzacoalcos (Co-AHT-zah-co-AHL-cos), a swampy little port where the Coatzacoalcos River empties into the gulf near some of Mexico's richest oil fields.

The town was transformed into an easy-money El Dorado by frenetic growth and contruction in the 1970s and early 1980s under the free-spending administration of president Jose Lopez Portillo. More than 50 plants and factories sprang up, almost all tied to oil and its derivatives. Tens of thousands of workmen flooded in, often bunking six and seven to a high-priced room.

The population jumped from 80,000 in the 1960s to more than 250,000 by 1980. Workmen, many without their families, gave Coatzacoalcos a reputation as a hard-drinking, quick-fighting oil town, with shantytowns springing up around the edges.

Several professors from the local branch of the University of Veracruz warned that such swift, unplanned growth carried dangers for the environment, and that the oil money could one day dry up.

"But nobody listened to those warnings," recalled Lorenzo Manuel Bosada, a biologist in the city government's ecology section. "They held up a world of fascination and wealth. They told us we were supposed to prepare for administering wealth, and so nobody listened to the warnings."

Jaime Quintanilla, president of the Chamber of Commerce, remembered: "There was no time to think. We were all so busy."

"And now we have the consequences," said Francisco Mata, a professor and former national legislator who has become an advocate for environmental cleanup. "People didn't realize. I don't say it was bad will. It was carelessness. Now that oil prices have fallen, which are the basis of the economy, everybody is wringing his hands."

The illusion of limitless growth was shattered in two stages here, residents recall. The first came when de la Madrid became president in December 1982, promptly cutting back ambitious spending plans that included more petrochemical facilities for Coatzacoalcos.

Many boom-time workmen's construction jobs came to an end. Thousands returned to the farmlands they had left. But thousands more, whose families had joined them, became permanent residents, straining city services and pushing unemployment to an estimated 30 to 40 percent.

"They thought it was going to be something grand, and it turned out to be an illusion," said Santos Senteno. His loaders' union used to send 800 members out on 12-hour workdays and now has trouble finding work for 400 remaining members.

Quintanilla said the full effect of de la Madrid's construction cutback was cushioned for a time by a decentralized purchasing policy of the government petroleum combine, Mexican Petroleum, or Pemex.

But falling oil prices have curtailed the Pemex largesse. The Mexican government depends on oil sales for 70 percent of its export earnings and half of overall government income. "Now we are going to feel it," Quintanilla said.

Mayor Figueroa added: "It is like the rich man's son who never realizes the time of his father's abundance is over. He keeps on spending at the same rate without realizing it's all over."

People here have realized now, and they already have paid a price environmentally. An article in the Mexico City newspaper El Universal on the area began:

"The bass and crab have died. The pelican made its cemetery on a pestilent beach, where a layer of crude oil fouls the river and heads for the sea. The wealth has ended, together with the big plans. It has passed, like a dream passes."

Bosada said a study by university professors and municipal experts, in cooperation with Pemex scientists, showed lead, mercury and other metals in the Coatzacoalcos River, along with quantities of petroleum in various stages of refinement accidentally spilled in an average of two incidents a month.

The Teapa River, which flows by the Pajaritos petrochemical refining and loading complex and into the Coatzacoalcos, has a red-wine hue, the effect of the sun reflecting off a perpetual oil slick. Its banks are coated with black muck and nearby trees have shriveled and died.

"Everything is dead, all dead," said Jose del Carmen as he guided his boat along the waterway and pointed out a fish floating belly up.

"I always said I would keep on fishing until the sea dried up, but they put all this crap in the water, and so . . . " He turned his palms up in a gesture of futility.

Nearby, black waste slopped into the Coatzacoalcos River out of a concrete ditch leading from the Pajaritos complex. A two-year-old study by scientists made public last month showed the river contains potentially carcinogenic agents, according to the Center for Ecodevelopment, a local scientists' group that coordinated the study with Pemex.

Pemex officials declined to comment on the pollution around their plants. But Rafael Marquet, a local Pemex spokesman, said that after the study became known the company has undertaken a number of projects to treat wastes before they flow into the river.