Five years ago, when the industrial age struck here with a vengeance, this swampy, fly-ridden land was far from prepared.

Once the seat of Mexico's magnificent Olmec culture, the countryside had turned to quiet, prosperous cattle and cocoa bean farming. Forever ruled by an appalling heat, urban life followed that slow rhythm of siestas and evening strolls.

Then the bogs outside Villahermosa were found to be hiding oil reserves that thrust Mexico among the world's oil giants and into the sights of petroleum speculators, bankers and spies.

To exploit the wealth, an army of more than 30,000 engineers, drillers, electricians and construction workers swarmed over the state of Tabasco. Straw hats turned into hard hats and buggies were shoved aside by giant trucks.

This world of a hundred lagoons has been transformed. It now produces three-quarters of Mexico's current 1.2 million barrels of crude per day.

Villahermosa, the capital of Tabasco, bustles and stirs like a frontiertown and has that giddiness that comes with the promise of instant wealth. "I'm seeing more new faces and shops and cars than I saw in all my life," an elderly saddlemaker said.

Yet, for all the euphoria of Mexico's bankers and petroleum technicians, the oil rush has brought an economic and social crisis to the Mexican "gold strip" that goes deeper than cultural shock and may be harder to deal with than the contaminated air or the ubiquitous oil spills in the lagoons.

The avalanche of oil men here was followed by another of entrepreneurs, peasants, prostitutes and thousands of unemployed who had heard about this promised land. The downtown bus station is humming with new arrivals, obviously impoverished men with as little as a shopping bag or as much as their whole family.

For every job in the area, one recent government study showed, there are seven applicants, at least five of whom are newcomers.

Neither Villahermosa nor nearby Coatzacoalcos, in the heart of the new petrochemical industry belt, is able to cope with the influx. Villahermosa's population, weary town officials explained, has doubled to at least 250,000 while nearly three-quarters of its 1977 budget of $3 million was spent on salaries of teachers and municipal employes alone. The town, they said needs more than 20,000 houses.

Coatzacolcos, according to the mayor's office, has sprouted 23 slums and only one-third of the 150,000 people have running water, a sewage system or electricity.

The question of who is responsible for this urban havoc is leading to friction among local and federal officials and Pemex, the state oil monopoly in charge of all stages of the petroleum business.

The municipal authorities feel the situation was predictable from the moment the government made the all-out commitment to exploit the area and development should have been adequately planned. Their own hands they say, are tied by their minute budgets.

State Gov. Leandro Rovirosa has frequently criticized Pemex which like an occupation army, has federal carte blanche to dig, drill, or build roads wherever it wants. Rather than wealth, Rovirosa charged, the government, through Pemex, has brought inflation, shortages and delinquency. Rents have more than tripled and stores have marked up their goods about 30 percent higher than Mexico City.

At the Ministry of Planning branch office hastily set up here, the feeling is that "gross distortations" were perhaps inevitable. "Just look at Pemex spending nearly $2 billion in 1978," said a planner. "It's obvious we have to strenghthen the role of government here and act quickly."

Even planning is difficult however. "Pemex changes constantly and moreover absorbs everything", he went on. "We can't get construction materials, cement, wire.Everything grows so fast, just last week at lunchtime we had to change a development project we had finished at breakfast because a major new well was found in the area."

Despite the resentment of many Tabascans, oil and the excitement of discovery dominate everything. It is most dramatic at night when the skies are lit up with huge gas flares for which the processing plants and the pipes are still inadequate.

In the daytime in the Pemex offices, engineers talk over the radio with the rigs, pinpointing the size of the wealth. Pemex is big and its men have begun to talk in American-style superlatives. "Over at Cactus we're building the largest gas sweetening plant in the world," they say, "and at Pajaritos the biggest petrochemical complex of Latin America is almost ready."

The Pemex men talk and act with the confidence of people who have been told that they are the saviors of the economy and the panacea for most of Mexico's ills.

"I know that a host of people hate us," said Pemex engineer Manuel Cinta, an aide to the district superintendent, "but we are here to get the oil out of the ground. The idea is to spend our money on production, not on social work. What we're doing is essential for the whole country."

That sense of mission is also clear in the fields, where the men slosh through mud and oil in overwhelming heat and often work afloat to cope with the swamps. At the Cactus gas sweetener, engineer Luis Puig said he has learned to live with the terrible sulphur stink because he is excited about the plant.

Five miles away at the Samaria Separation Station, the roar and the heat of the turbines, pumps and 40-foot gas flares seemed like hell itself. But Quirino Banos, 25, the engineer in charge, asked where else would he get a chance to do pioneering work like this.

Pemex, however, who do not dare speak out loud. One Iong-time engineer - he asked that his name be changed to Fernandez - feels the price Mexico is paying for progress is to high.

"It's not only the mess in the towns," he said in an interview. "Ten years ago when I came here, the rivers and the lagoons were pure. At one of my rigs I used to be wakened by a pack of 30 monkeys. Now there isn't a tree left there, let along animals."

That message is also coming from the farmers of Tabasco, the most fertile state in the republic. Near Cunduacan, one of the major oil fields, peasants organized against the construction of an ammonia plant which was certain to disrupt their lush banana and cacao groves. For days on end they set up roadblocks, meeting Pemex workers with machetes and old-fashioned shotguns. The ammonia project was moved to another site.

In Villahermosa, recently, demonstrators arrived from Mecuacan, where 1,500 families live off oyster farming in a vast lagoon. The oil spills had ruined everything, they said. "We're going to kill those Pemex guys if they come back," they shouted, waving the blackened, dead oysters.

"We are just going to have develop more rationally," reacted a federal official after talking to the men from Mecuacan. "We must continue developing agriculture as well. We can't have on big ghost country here after the oil is gone."