Rio de Janeiro — In the outback of Brazil, a tri-faceted development project on a patch of land somewhat larger than the state of Rhode Island holds the potential for paying off what now amounts to a $90 billion foreign debt.
The ''Greater Carajas Project may prove to be the country's emancipation from its strangling foreign debt,'' says Olavo Egydio Setubal, president of Banco Itau, Brazil's second-largest commercial bank.
At least it has that potential. The mineral, lumber, and agricultural project is in its infancy. It isn't expected to get fully under way until 1985. Nonetheless, it is receiving considerable attention. The project is located in the northeastern state of Para, where there is an area of 400 square miles that constitutes what may be the greatest concentration of minerals in the world.
A complete survey of the Carajas site won't be ready for another year or two; the figures given here are based on preliminary examinations by US and Japanese geologists.
* Iron-ore deposits, in a more advanced state of exploitation than the other minerals, are estimated at 60-70 billion tons, about a third of which is over 66 percent pure iron content, the highest in the world.
With world iron-ore reserves totaling 251 billion tons, of which the Soviet Union possesses 110 billion tons, Brazil is in second place.
* Carajas also contains large high-grade deposits of manganese, estimated at 60 million tons; copper, from 1.2 to 1.5 billion tons; uranium; nickel; cassiterite (tin ore); cobalt; bauxite; platinum; niobium; gold; silver; argon and xenon gases used by the chemical industry; and up to 10 billion tons of open-pit mineral coal.
As the United States depends to a large extent on imports of cobalt, tin, niobium, bauxite, and platinum, Brazil is planning to create ''strategic reserves'' of the metals to meet US demands.
Mineral development in the Carajas project is in the hands of Companhia Vale do Rio Doce (CVRD), which is known as the best managed of all the 300-odd government-controlled companies.
Until now, no American steel company has contracted to purchase any of the Carajas iron-ore production, which is scheduled to reach 5 million tons in 1985, increasing to 35 million tons by 1989. However, future sales contracts have already been closed with Japan, South Korea, Italy, Belgium, Spain, France, Argentina, and several Arab countries for delivery of 27 million tons annually over the next few years, according to the list submitted in 1982 by Eliezer Batista, president of CVRD, to the World Bank in connection with a $305 million iron-ore development loan.
Up through the end of July 1982, $922 million had been already invested in iron-ore development, covering about 30 percent of the basic work. The entire iron-ore development project will require an estimated additional $4.8 billion investment. A total of $1.8 million in loans has already been approved from the European Economic Community, Japan, the World Bank, the Export-Import Bank in Washington, West Germany, and the United States. The remaining $3 billion will come from the CVRD and Brazilian banks.
The Carajas area also contains more than a million acres of virgin timberland , mostly hardwood. It is part of the region's Amazon tropical forests, which constitute 20 percent of the world's timber reserves and contain more than 100 trillion cubic yards of commercial lumber valued at over $30 billion.
With the favorable climatic conditions, the trees enjoy one of the fastest growth rates in the world. Yet Brazil's annual lumber exports rarely reach $1 billion. So far, proposals to open the area up to exploitation with foreign risk capital have been attacked by nationalistic elements.
Finally, the Greater Carajas Project envisages the development of agriculture crops suitable to the tropical Amazon region, such as rice, cassava, rubber, soybean, corn, sugar cane, tobacco and others.
The major stumbling block to the project is the lack of infrastructure. Roads , a 600-mile railway, an enlarged port, and housing facilities will tack another may not find raising such a sum easy.
But, Brazilians are hopeful that the lure of the additional exports from Carajas - estimated at $15 billion annually at today's prices - beginning in 1990 will enable them to obtain the funds through loans and joint ventures. The figures speak for themseves: An additional $60 billion should allow $150 billion to $200 billion in increased exports over a 10-year period. It may be one of the best options Brazil has for eventually repaying its foreign debt.