Crippled by world oil prices and anxious to claim its place in the developed world, Latin America is preparing to enter the realm of nuclear energy in a big way.

Before the end of the 20th century, six Latin countries expect to be running their own nuclear power plants. At least three others plan to have small nuclear research reactors.

Within the next three years, Brazil is expected to possess the material to build an atomic bomb. Argentina, with one nuclear energy plant already operating and another under construction, says it could develop bomb technology any time it want to.

Although both say they have no intention of building bombs, neither Argentina nor Brazil has ratified key portions of Latin America's own nuclear agreement, the 1967 Tlatelolco treaty prohibiting nuclear weapons signed last week by the United States. Additionally, despite heavy U.S. pressure, neither has signed the nuclear Non-Proliferation Treaty.

"A concern exists" over mushrooming nuclear growth without adequate safeguards, one U.S. diplomat here said. But the Latins, particularly Brazil and Argentina, maintain they have their own safeguards, written into bilateral agreements with the countries that supplied their technology. Virtually none of that technology, and little of the Latins' nuclear equipment, has come directly from the United States.

Most of it has been purchased from Europe and Canada or has, to a growing degree, been traded among the Latins themselves.

Argentina, long the Latin nuclear leader with research dating back to the mid-1950s, signed an agreement last month to supply Peru with a low-power training reactor by next year. The Argentines have also committed themselves to providing limited nuclear technology to Ecuador and Uruguay, neither of which currently has a significant nuclear program.

Argentina's own program has undergone several setbacks lately, largely the result of a brain drain of trained scientists seeking higher salaries and escaping from a series of governments that have tended to let politics interfere with research. Oscar Quihillalt, director of the Argentine National Atomic Energy Commission for nearly 20 years, is now chief nuclear adviser to the shah of Iran, whose pay scale has also drawn many of Quihillalt's Argentine co-workers.

Still, Argentina's 300-megawatt, West German-made reactor, opened in early 1975 near Buenos Aires, remains the only energy-producing facility now on the continent. Its efficiency and safety records are among the best in the world.

A second power reactor, twice the size of the first, is being purchased from Canada and is scheduled for completion in 1981.

In recent published interviews, the current Argentine nuclear chief, Admiral Carlos Castro Madero, has said that his country "is in a position to make a nuclear explosive" and that the decision not to do is "a political and not a technological one."

According to other nuclear experts, however, Argentina would not only have to violate safeguard purchase agreements with West Germany and Canada, but would have to develop some extensive new facilities on its own to build a bomb. Both its power plants are designed to operate with natural uranium and a heavy water moderator - meaning that their radioactivity wastes are not highly charged and it would take expensive reprocessing to turn them into explosives.

Both Chile and Venezuela have operating research generators - non-power facilities primarily used for medical purposes. But they, and Mexico, are well on their way to having their own power plants. Venezuela, which fears its oil money will run out before long, plans to have at least 14 nuclear power plants on line by the year 2000.

Colombia, believed to be rich in uranium like most of Latin America, recently signed a contract with a French company to explore for radioactive mineral deposits. The Colombians are now developing a feasibility study for a nuclear energy plant, and hope to begin construction in 1990.

By far the continent's most ambitious nuclear program, however, is in Brazil.Bled nearly dry by the cost of foreign oil, which supplies 80 per cent of its petroleum needs plans are under way for eight West German reactors that will take care of 25 per cent of Brazilian power needs by 1990.

That program has gone forward despite United States opposition to the type of technology planned - reactors using enriched uranium, the stuff of atomic bombs. Both the Brazilians and the West Germans have bucked President Carter's disapproval and last week they ratified the nuclear agreement they signed in 1975.

Carter's goal has been to restrict the number of nations with the technology to produce enriched uranium, and thus to make bombs. At the same time, he has prohibited sale of United States nuclear supplies to any nation that refuses to sign the Non-Proliferation Treaty. Canada's support of that policy, and anticipated refusal to sell Argentina heavy water for its new nuclear plant, is expected to pressure Argentina into signing.

But Brazil has remained adamant in its opposition to what Brazilian nuclear head Paulo Nonguira Batista last week called an "unbalanced, unequal and wicked" document.

Latin reluctance to accept the treaty is a combaination of resentment at what are viewed as United States-imposed rules and a sense of insult at the implication that the Latins would not respect their own safeguard documents. In addition, there is a psychological fear of exposing themselves to each other's potential weapons superiority.

A January editorial in Brazil's leading newspaper, O Estado, said the Brazilians were afraid that signing an international accord "would leave the nation potentially inferior, in military terms, in relation to Argentina." An Argentina with a bomb-building capability that Brazil did not have "could pose political-psychological problems in international conversations."

But the long-held mutual suspicion between Argentina and Brazil and their rivalry for Latin domination are being rapidly replaced by offers to share technology and a united front against outside attempts to control Latin nuclear programs.