BY MICHAEL ASTOR
  Associated Press

  RIO DE JANEIRO - Setting aside a swath of Amazon rain forest bigger than Belgium, President Fernando Henrique Cardoso signed a decree Thursday creating the world's largest tropical national park.

  The Tumucumaque Mountains National Park covers a virtually uninhabited region of virgin rain forest in the northern Amapa state.

  ''With the creation of Tumucumaque Mountains National Park, we are ensuring the protection of one of the most pristine forests remaining in the world,'' Cardoso said in a statement. ``Plants and animals that may be endangered elsewhere will continue to thrive in our forests forever.''

  Deforestation has destroyed about 15 percent of Brazil's Amazon rain forest, which today covers about 1.35 million square miles. Roads have accelerated destruction of the forest by providing access for settlers, prospectors and loggers.

  The new park is about 568,000 acres larger than Slonga National Park in the Democratic Republic of Congo, until now the world's largest protected tropical reserve.

  The presidential decree came four days before the Johannesburg Earth Summit. At the summit, he is expected to announce the Amazon Region Protected Areas
  program, which puts 200,000 square miles, including Tumucumaque, under federal protection.

  GENETIC PROTECTION

  Cardoso also signed a series of measures regulating the use of genetic material gathered from Brazil's immense variety of plant and animal species.

  Tumucumaque, which means ''the rock on top of the mountain,'' in the language of the Apalai and Wayana Indians, is 9.6 million acres of forest-blanketed mountains with occasional outcroppings of granite rising as high 2,300 feet.

  It is full of waterfalls and crisscrossed with white-water rapids and rivers that are impassible even during the dry season, making it one of the few remaining regions
  largely unchanged by humans.

  Jaguars, sloths, giant armadillos, anteaters, harpy owls and black spider monkeys inhabit the forest, and scientists know of at least eight species of primates, 350
  species of birds and 37 types of lizard there.

  SURPRISES SEEN

  But they feel certain that further research will turn up surprises.

  ''The park is very important because it helps consolidate one of the world's last roadless wildernesses,'' said Roberto Cavalcanti, director of Conservation International in Brazil, which helped create the park.

  ''I don't have any doubt the park will yield new species,'' said Jose Pedro de Oliveira Costa, secretary for biodiversity and forests at Brazil's Environment Ministry.

  Costa said he hopes millions of dollars in promised funding from the World Bank and Global Environmental Facility will help Tumucumaque avoid the fate of other
  Amazon parks, which have been vulnerable to illegal mining and logging.

  Initially, the park will be open only to scientists, who will study how best to combine tourism with preservation.