Maracaj'u, Brazil — ROBERTO Wurtheim, college graduate, family man, and fourth- generation German Brazilian, is typical of Brazil's new breed of frontiersmen. A ``gaucho'' from the cattle and grain lands of southern Rio Grande do Sul State, he and his family are homesteading a 5,000-acre patch of rolling countryside here, planted largely with soybeans.
Like frontiersmen the world over, the Wurtheims left behind a familiar way of life that had suited three generations of Wurtheims before them.
Selling off a 500-acre farm in their native state, they bought this sprawling spread in an area of Brazil that is suddenly opening up to a new breed of homesteaders. Those coming to Mato Grosso include many Brazilians of German ancestry like the Wurtheims.
Until a decade ago, there were few roads and few conveniences in this wilderness.
Now roads crisscross the area. Pioneers are moving in daily. And as they do, land prices are soaring.
``We got here just in time,'' says Mr. Wurtheim. He adds: ``I doubt that I could have afforded this land if I had waited another year or so. I would probably have had to go even further north to find what I could afford.''
As it was, the Wurtheims came 1,500 miles north to their new land -- the sort of trek familiar to generations of homesteaders the world over. But today's frontiersmen make their moves with an ease that would astonish pioneers of a generation ago. Gone are the days of the covered wagon, the walking into the wilderness.
The Wurtheims -- Roberto, his wife, Celia, and their four children, together with assorted pet dogs and cats -- came here three years ago in their new Brazilian-made Chevrolet and a rented Ford pickup truck that brought most of their household belongings.
Getting the land ready for cultivation, however, has been a lot more like traditional pioneering. A tractor that had been ordered was delayed in arrival and ``a lot of the work I did at first was by hand and with a borrowed but antiquated tractor of a neighbor,'' Wurtheim says.
Simply preparing the land of trees, stumps, and overgrowth took a year's time. But the hard work has been worth it.
``Last year's crop,'' he says, ``was better than I expected. I earned about 30 percent more than I estimated and I think that 1985 will be equally good.''
Wurtheim is one of those playing a role in Brazil's soybean revolution. Before 1970, the nation produced very few soybeans. Now Brazil is the world's second-largest soybean exporter, earning more than $2 billion a year from the crop.
It was difficult for the Wurtheims to uproot themselves for the frontier. But they felt it was where their future was.
``We would not have come,'' says Roberto Wurtheim, ``If I had not felt there was real opportunity for me and for the family and at the same that we are making our mark in building Brazil.
``I don't mean to sound overly patriotic, but then again why not? But I do feel it is important to build Brazil. It's our homeland now. It's our country. It is up to us to do something to ensure its growth.
``It is our way of having a part in something we think important.''
The Wurtheims were also pleased to discover that a half-dozen of the nearest 15 farms are owned by other German Brazilians, most of whom still speak German, in addition to Portuguese.
``We spoke German at home as a matter of course as I was growing up,'' says Wurtheim, ``but we use Portuguese in our household today.''
The Brazilian government officials in Bras'ilia, the capital, estimate that 200,000 settlers a year are moving into areas like Mato Grosso and Rond^onia -- still sparsely populated regions.
It is an area of almost a million square miles but so far it has a population of less than 3 million, according to Heitor da Sousa, an official in Campo Grande, capital of Mato Grosso do Sul.
``We expect a continuing influx over the next 10 years,'' he says. ``This is where Brazilians with vision want to go.''
That may be too chauvanistic a view, for many perfer life in the eastern industrial and cultural centers. But for many adventurers and stout-hearted souls, the frontier is the place to be.