Like North Americans of an earlier era, Brazilians like to speak in superlatives. Theirs is the biggest country, with the largest population and the most industry in Latin American. Now, on a site 10 miles from this southern border town. Brazil, with the help of neighboring Paraguay, is building the biggest hydroelectric dam, not only in Latin American, but in the world.

Itaipu dam, the name means "singing rock" in the local Guarani Indian language, is to be completed in 1983. It will have gouged more than 60 million cubic yards of rock and dirt from in and around the Parana River and replaced it with 16 million cubic yards of concrete.

It will provide 12.6 million kilowatts per hour of power, a third again as much as today's largest hydroelectric facility, Grand Coulee in Washington state.

That is enough electricity for all of New York, including New York City. The power will travel throughout southern Brazil and into the heart of Brazil's industrial district at Sao Paulo.

Since construction began more than two years ago, progress has been largely limited to digging a huge, mile-long, crescent-shaped gash on the Brazilian side of the river. Next year, the ends of the crescent will be blasted away and the Parana will flow off to the side leaving the main dam site dry for construction.

For most of its route through south central Brazil, and through Argentina to the sea at Buenos Aires, the Parana is wide and sluggish, a rust-colored ribbon that picks up Georgia-like red clay inland and dumps it in a several-miles-wide delta between Argentina and Uruguay.

But 100 miles north of here, the river begins a 300-foot drop that will provide the power for Itaipu's 18 giant turibines.

More impressive than the building site - which at this point looks like little more than a big riverside hole in the jungle, surrounded by piles of rock, sand and machinery - are support structures to house, feed and care for 18,000 laborers and professionals.

The workers get free housing - ranging from four-to-a-room barracks for laborers, to two-bedroom houses in prefabricated villages for married professionals - subsidized food and free medical care and entertainment.

Many of the workers belong to the rapidly growing Brazilian subclass called barrageias, or dam workers, who spend years travelling among construction projects in the wilderness where they make more than twice the national minimum wage of $70 a month.

Boredom is epidermic. Liquor is forbidden within the work and living areas as are women not employed by the company. Although makeshift villages of enterprising prostitutes have sprung up between the camp and town - with the company's doctors providing unofficial medical care for the women - security officials say they wage a nerver-ending battle to keep them from being smuggled into the barracks.

Just last week, a company official said, guards hauled three women out from under the seat of a dump truck being driven through the camp gates.