Standing on a bridge over the Parana River dividing their two countries, the generals heading Brazil and Paraguay jointly pushed down a lever today that lit up a pair of glass sculptures depicting the flags of the two South American nations. Simultaneously, an engineer threw a switch to start two of the 18 turbines of the massive Itaipu hydroelectric dam looming behind them.

With that gesture by Presidents Alfredo Stroessner of Paraguay and Joao Baptista Figueiredo of Brazil, 1.5 million kilowatts coursed through transmission lines into a chain of power substations and on to Sao Paulo, 500 miles to the northeast.

At full capcity, Itaipu, the largest hydroelectric dam in the world, will generate 12.6 million kilowatts, better than a quarter of the energy this nation of 130 million people now consumes.

A month from now, in the extreme north of Brazil, another hydroelectric colossus, Tucurui -- plunked down in the middle of the Amazonian rain forest -- will begin to pump its eventual capacity of 8 million kilowatts into the sorely underdeveloped Amazon basin.

Begun more than a decade ago, Tucurui and Itaipu are two of Brazil's greatest works, which despite their collective $23 billion price tag are said to be necessary to decrease Brazil's dependence on imported petroleum.

The works themselves are monumental, born of an era Brazilians call one of Pharaonic works after the grandiose vision of the military men who have ruled Brazil since a coup in 1964, and who have been determined ever since to turn this underdeveloped country into a world superpower.

Itaipu's walls tower more than 900 feet above the ground, about the height of a 60-story building.

The 75 billion kilowatt hours per year Itaipu will produce could save Brazil the equivalent of 600,000 barrels of petroleum per day -- two-thirds of the country's current consumption.

The junior partner in the deal, Paraguay, with a population of only 3 million, can absorb no more than 5 percent of the giant plant's energy. However, according to the bilateral pact, Paraguay has title to half Itaipu's power. Thus Brazil will end up buying back the energy its neighbor can't use.

Next month, when the Tucurui dam comes on line, just the first two turbines could furnish energy for a city of 3 million. At the height of construction, 37,000 men worked on the dam. It sits on the Tocantins River, reportedly the largest ever to have been dammed.

These two works have been lauded as vital, "a model for all countries desiring progress and development," as Figueiredo said at the inauguration. Yet they were built amid controversy. Respectively the largest and the fourth-largest hydroelectric dams in the world, they have been denounced as far too large for a nation squeezed by foreign debt and battling the effects of world recession.

They have also been labeled damaging to the environment. Itaipu's reservoir covered over a stunning series of seven water falls. The herbicides used along the Tucurui project's transmission lines have been linked to human and animal illnesses and crop destruction in the backland villages of the Amazon.