Over the past decade while Argentina stumbled from crisis to crisis, Brazil has gradually acquired an empire.

The richest country in Latin America at the end of World War II, Argentina steadily declined through years of political turmoil. Brazil, on the other hand, has emerged as an economic and political power thanks to the single-mindedness of its military governments, which have elevated "manifest destiny" to the status of a religion.

Uruguay, Paraguay and Bolivia have become Brazilian satellites, and now Brazil is reaching out to Ecuador and Chile.

"Manifest destiny" has always figured porminently in the Brazilian view of South America, as every country bordering the giant nation has learned at its cost. The only countries that did not lose territory to Brazil during the 19th and early 20th centuries were Chile and Ecuador - and this only because they do not share a common border with Brazil.

Through threat or treaty, Brazil's neighbors have ceded it 248,198 square miles of land.

"Big Brazil" has been a cornerstone of military planning ever since the 1930s, but it was not until after World War II that the Brazilian Advanced War College began to elaborate a geopolitical doctrine that divides responsibility for policing the hemisphere between Brazil and the United States.

One of the corollaries of this doctrine is an open-ended definition of frontiers. Gen. Golbery do Couto e Silva, the Brazilian military's Chief ideologist, maintains that the borders of nations are not limited by physical barriers because there are ideological, economic, and "living" frontiers as well.

Ideologicaly, Brazil's Doctrine of National Security, as it is called, has been religiously copied, down to the last administrative detail, by rightist regimes in five South American countries. The titles are slightly different, but there inevitably is an all-powerful security apparatus and a military council of state that chooses the president and the judiciary and legislates by decree.

Brazil also has encouraged "living" frontiers in Uruguay, Bolivia and Paraguay - particularly the latter, where some 80,000 Brazilian colonists have settled on Paraguayan land.

In this region, between the Iguazu Falls and the upper Parana River, the most common spoken language is Portuguese, transactions are carried out in Brazilian cruzeiros, and the law is Brazilian. Land, titles, for example, are processed by Brazil's Agrarian Reform Institute.

Far from objecting to this Brazilianization, the Paraguayan government has encouraged land sales to Brazil, even when they entail evicting Paraguayan peasants living on the land.

In one recent incident near Villarica, 250 peasants were forced at gun points to abandon 2,500 acres so a Paraguayan real estate firm, Ruis and Jorba, could sell the land to a Brazilian company. One of the largest local landowners, Gen. Otello Carpinelli, head of Paraguay's II Military Region with headquarters in Villarrica, has been accused of using troops to carry these evictions.

Twenty foreign companies, mostly Brazilian, now own 40 per cent of Paraguay's land, the country's principal source of income and jobs.

A similar process is being repeated in northeastern Bolivia, in the rain forests of the Beni, where Brazilian farmers have settled on Bolivian lands. Wealthy Brazilians are also buying up large tracts of cattle land in northern Uraguay, although this "living" frontier is not as advanced as those in Paraguay and Bolivia.

To support pentration of its neighbors' Brazil's military regime has embarked on an ambitious program of roads, railroads and ports to connect Bolivia's eastern lowlands with Santa, the southern Brazilian port, and to link Paraguay's capital, Asuncion, with a giant new Brazilian port at Rio Grande. The Brazilians have also built highways connecting southern Brazil with Uraguay's routes 5 and 6, which crisscross the country.

Although temporarily stalled for lack of funds, Brazil's trans-Amason Highway is eventually to reach the jungle frontiers of Peru, Colombia, Venezuela and the Guianas.

Brazil also hopes to penetrate Chile through a link-up with Bolivia's railroad system, and the Ecuadorian government has signed an agreement to develop a route connecting Brazil's Amazon port, Manaus, with Ecuador's port San Lorenzo on the Pacific Ocean.

The drive behind this costly program is Brazil's ambition to dominite the Plate River Basin, which contains 80 million people, one-third of South America's territory, 10,000 miles of navigable rivers, enormous mineral riches and a hydroelectric potential of 60 million kilowatts. Because of Argentina's political instability, Brazil is well on its way to realizing this ambition.

Although landlocked Paraguay still moves 90 per cent of its exports, through Argentina ports, Paraguayan President Alfredo Stroessner has given the Brazilians the key to the Plate River Basin by agreeing to the construction of a $7 billion hydroelectrical complex called Itaipu on Paraguay's Parana River.

The country that controls this queen of rivers, with its 33 million kilowatt hydroelectrical potential and tributaries reaching into four countries, can dominate the region.

Argentina, which has also been negotiating a joint hydroelectrical project on the Parana River, was outraged by Asuncion's seeming betrayal, claiming that Itaipu seriously jeopardizes the feasibility of a proposed Argentine complex downriver. But as a Paraguayan engineer pointed out, while Argentina proposes, Brazil disposes.

Paraguay even committed itself to sell Itaipu's 12.6 million-kilowatt output to Brazil for the same price for 50 years - the price being 1/8 the rates now charged in the United States.

According to the Brazilian Ministry of Mines and Energy, Itaipu will produce energy that is "25 or 30 per cent cheaper than the cheapest energy available in Brazil." As for Paraguay, the Stroessner regime flaiclaims that it is "not interested in making money" on Itaipu.

While many Paraguayans are privately bitter about "the sell-out to the Brazilians," few are prepared to protest after Roberto Thompson Molinas' experience. The former editorial editor of Asuncion's largest daily newspaper, Thompson Molinas spent four months in prison because his paper editorialized against the terms of the contract.

Brazil has a similarly advantageous price-and-supply agreement with Bolivia for natural gas.

Moreover, Bolivia's pro-Brazilian military regime is cooperating in blocking Argentine designs on the rich iron deposits in the Mutun fields of eastern Bolivia.

Although Brazil has more than enough iron ore of its own, with some 150 billion tons in reserve, Brazil won Bolivian agreement for a joint venture to exploit the Muntun deposits, including a plant that will semi-process 500,000 tons per year for sale to Brazil.

Argentina, which imports iron ore, was the obvious customer for the Mutun iron, particulary since its pricipal steel complex, San Nicolas, is located on the Paraguay River down-stream from the Muntun river port at Puerto Sazar.

But instead of offering to joint venture the partial industrialization of the iron, as the Brazilians did, the Argentines demanded that Bolivia sell them the crude ore.

So once again, the game has gone to Brazil.