"The Biennal is a party," organizer Roberto Muylaert told guests at the opening of South America's largest cultural event.

Architect Oscar Niemeyer's immense Biennal pavilion is once again bursting with paintings, sculptures, installations and performances -- works by 700 artists from 46 countries. There were good-natured political demonstrations and even a sneak "intervention" by uninvited artists who went wild on a stretch of blank wall with cans of paint.

The Biennal, which officially opened Friday, confirms that Latin American art is acquiring a vitality and identity increasingly independent of American and European models.

Brazilian artists show phonographs with three-foot tone arms and tiger-skin-colored kitchens where even eggs in the icebox are painted. A Peruvian exhibit satirically reinterprets old masters such as Rembrandt's "Anatomy Lesson," where a sinister uniformed officer now dissects his prisoner, reminiscent of Che Guevara.

Young Argentine painters are also enjoying new political freedoms. "Our painting is now a comic tango -- an oscillation between humor and anxiety," said Alfredo Prior. "Latin painting is so much more vital."

It also confirms that, although half the works are by Brazilian artists, Sa o Paulo's 18th art Biennal is firmly established on the international circuit. This time it includes the presence of American composer John Cage and a striking exhibit of American artists who explore the frontier between art and technology.

"There's no doubt that the art of the Americas -- North and South -- is more energetic today," said Biennal president Muylaert, who believes "art is freer here -- more experimental."

Brazilian organizers have shown no reservations about adapting installations to available space. The seven-foot-high gray robot figures of Jonathan Borofsky's "Seven Chattering Men and One Flying Man" incongruously shared the floor with a "magic ritual circle" of Brazilian synthesizer musicians.

Expressionist painters found their works crammed into three immense 120-yard-long corridors that leave visitors gasping at the unrelieved acreage of canvas. Many painters demanded more space for their work.

But the Biennal's curator, Sheila Leirner, said the idea of her "big screen" for Expressionist art was "to create an analogy of the present situation -- if you find there's just too much of the same art then that's your critique."

Retorted a visiting American critic, "We all know that, but you don't have to hit us over the head with it. It's discouraging to look down a corridor like that."

The most striking American exhibit is the group show "Between Science and Fiction." The organizers have resisted the temptation to overwhelm with laser art and sophisticated equipment.

"We're interested in art, not hardware," said the show's joint curator Robert Atkins. "Anything that's called computer art seems qualified, as if it couldn't stand up in a general context."

Instead there are political pieces like Hans Haacke's "We Bring Good Things to Life" -- a marble rocket column whose nuclear warhead is a bronze bust of Ronald Reagan straining skyward. Nancy Burson's computer graphics portrait blending the faces of U.S. and Soviet leaders is a reminder of the underlying nuclear anxiety that emerges more strongly in separate European exhibits.

"People ask me if I believe in nuclear disaster -- in our dreams it's already happening," says Danish artist Ole Sporring, whose futuristic drawings show landscape in collapse.

When the United States pulled out of Brazil's 1969 Biennal as an artists' protest against the former military government, an exhibit by MIT's Center for Advanced Visual Studies was canceled. This year MIT is back in force, headed by Otto Piene and his 15-foot-high inflatable Icarus, which was exhibited in Washington in 1979.

"We are sharing what we have been invited to share, and good ideas have a habit of spreading," said Piene. Many of the pieces are about the artists' makeshift use of low technology, and the show's Brazilian joint curator Berta Sichel maintains "the medium doesn't matter." Nonetheless, artists in the group show suggest their rediscovery of technology through science fiction gives them a creative edge over the hundreds of Expressionist painters in the Biennal.

"I would sum all this up as stress art -- people don't have time anymore so they just try to cover surface as quickly as possible," said Titus Leber, one of the MIT artists. "I can't understand how most of this stuff got in here -- nobody likes it."

Ned Rifkin, curator of contemporary art at Washington's Corcoran Gallery, warns that massive exhibitions like the Biennal "are in danger of becoming boat shows. When you begin looking for styles and trends you miss the forest for the trees -- it will take months to soak all this up.

"There's everything from handicraft to sophisticated technology -- it's not a cohesive statement," said Rifkin, here for the show's opening.

He singled out the Norwegian Inge Bjorlo's installation "Rubber in Brazil" as one of the high points. In a gloomy, pungent interior draped with sheets of industrial rubber, ducts and inner tubes, visitors walk on black rubber shavings and bump into piles of giant truck tires. Some of the rubber began its life in Brazil's forests.

South America's only ethnic contribution is a powerful display of highly colored ritual masks from Bolivia collected by journalist and photographer Peter McFarren. The Smithsonian Institution plans to tour the United States with an exhibition of these masks. The exhibition also is planned to go to Europe.

"It's ironic that so much art is being brought here to the Brazilian Biennal whilst Latin America's genuine art work is being taken out to museums in Europe and the U.S.," said McFarren.