TWILIGHT seeps steadily into nightfall as the Sao Joao Baptista quietly slips against the battered wharf after its trip up the Amazon River. The stubby little riverboat has come 1,000 miles from the Atlantic. Its human cargo of 111 homesteaders, some of them children age two and three, wait apprehensively on the deck as boat handlers tie it up and customs agents come aboard.
Within 12 hours, the Sao Joao Baptista will be headed downriver bearing freshly harvested mangoes and other fruit of Amaz^onia.
The new homesteaders waiting on board are part of a human flood of Brazilians and foreigners sweeping into this steamy, vast, almost untapped, and largely untamed Amazon Basin.
The rush to this Wild West-like region -- some 2 million square miles or almost half of the country -- is a bit like that to the western United States 100 years ago.
It comes as the result of Brazil's massive development boom of the 1970s.
First, the 2,000-mile Amazon Highway was laid through dense rain forest to the northern states of Amazonas, Rondonia, and Acre. Then came the smaller highways and roads, which now carry thousands of pioneering Brazilians to new lives -- and possibly to new fortunes -- in the Amazon and the states of Mato Grosso and Mato Grosso do Sul.
The highway offered relief to people of the drought-ridden, overcrowded northeast, and opened a door to the Amazon's vast mineral and timber resources. The new settlers have helped turn Manaus, Boa Vista, Rio Branco, P^orto Velho, and Cuiab'a into boom towns.
Manaus itself has known an earlier rush of eager fortune-seekers. The discovery of rubber plants led to a mighty human tide at the turn of the century, but that westward move ended when rubber-growing began in Malaysia. Brazil's rubber boom went bust before World War I.
``At least 200,000 a year are migrating into this wilderness,'' says Ernesto de Aguiar, an official in the Manaus office of Brazil's Institute for Colonization and Land Reform. But he says there is no exact tally on the numbers of immigrants.
``They come from all parts of Brazil -- and elsewhere, too. I think a lot of them get a surprise when they arrive. They think, because there are highways and plane flights, that life here will be less difficult than it was on the frontiers of the past.
``How wrong they are!
``But I suppose the lure of the frontier gets them. I know. It got me. That's why I came here from Recife.''
Rodrigo Mendes Dias, an official at the Cuiab'a office of the Institute for Colonization and Land Reform, says: ``There may be other land frontiers around to lure the pioneer. But for the moment, Brazil is the world's most popular frontier.''
The frontier is attracting homesteaders, gold prospectors, and prosperous farmers from Brazil's south who want more land. It is attracting bankers and big international corporations involved in agribusiness.
But Brazil's west is still very much a frontier. In Cuiab'a, capital of Mato Grosso State, police say that they have a hard time keeping order, particularly on the edges of the town, which has grown 20-fold in population in just five years.
It is even rougher in Pinda'iba, 100 miles from Cuiab'a, where Police Sgt. Jos'e Piva says, ``The local saloon usually has at least one good fight on a Saturday and it is not uncommon to have some shooting as well.
``Don't forget we are on the cutting edge of civilization here. Things will change as the frontier gets tamed.''
The taming process is already under way. The highways that bring so many settlers are part of the process. Just as the railroads helped tame the West of the United States, the highways are doing it here. They bring fortune-seekers, homesteaders, and booksellers. Stores and gas stations appear along the highways. Many of the new businesses here are branches of some of Brazil's wealthiest chains.
The highways are perhaps the most important feature of Brazil's frontier.
``It is the highway that has made this pioneering possible,'' says Walter Sallas, a bank official in Cuiab'a. ``Not only has it made it easier to get here, it has made it easy to get food and other things to markets in the east. Spoilage and other delays are not much of a problem.''
Many of the new homesteads are very productive.
``Here at the bank, we have no qualms about giving credit to these homesteads. Most are good workers. But more important, we know that what they produce will sell and that it will get shipped to markets quickly. These people and their homesteads are good risks.''
Many of those who come are ready to begin farming immediately. Julio de Campos, governor of Mato Grosso, lauds these pioneers:
``They go to work the day they arrive. It is amazing how fast the crops come up under their tender care. They are pioneers, but they are farm experts, too, and they know what it is they want to do. They want to farm.''
In Mato Grosso and Mato Grosso do Sul, the main crops are soybeans, rice, sugar, corn, and beans. The soybean saga is perhaps the most exciting agricultural achievement on the frontier.
Five years ago, neither state produced soybeans. Today Mato Grosso raises some 7 percent of Brazil's soybeans, and Mato Grosso do Sul another 18 percent. Both states expect to double their production in 1985 and 1986. Soybeans have become one of Brazil's chief exports.
Further north in Amazonas State, it is a similar story. Sugar, rice, and spices, together with native Amazon fruits, are the main farm products. Homesteaders with 250 acres -- considered good-size farms here -- are turning in cash crops the second year on the land.
But there are concerns. The surge of population into previously untapped wilderness is beginning to take a toll on the region's ecology. Some of the farming techniques are primitive. Over the long range, such practices as slash-and-burn land-clearing could ruin the soil, agricultural scientists say.
``These are fragile soils and if maltreated they may give out in a year or so,'' says agronomist H'elio Barbosa da Lima. ``That doesn't have to happen and I know many good farmers who are using modern machinery and using lime and phosphate and other fertilizers to give nutrients to the soil.
``Ah, but I know other farmers who don't care, don't know better, and they are killing the soil.''
The problem, of course, is that the human tide is clamoring for land and there are not enough experts to help the new farmers, nor are all parcels of land the same.
``It may get better as time goes on, but in the meantime we will lose a lot of potentially good land,'' says Mr. Barbosa da Lima.
Other casualties of the new farming boom are the Indian tribes on Brazil's frontier. Tensions between the pioneers and Indians are rising as soil runoff from some farms pollutes Indian water supplies. And there have been Indian reprisals against settlers who have moved onto lands the Indians claim as their own.
Colonization official de Aguiar says that while pioneers ``are finding life here harder than they expected, they are proving generally to be good workers. The new homesteaders in Amazonas State, who have come here in the last five years, are responsible for the quadrupling of agricultural production in the state during these years.
``I would not be surprised if we have another quadrupling in the next five years.''