The army, navy and air force troops will use river patrol boats, helicopters and planes to crack down on drug trafficking and other smuggling activities on Brazil's 16,900-km (10,500-mile) frontier with 10 South American nations.
Much of the border is Amazon jungle that is hard to patrol and notoriously porous, allowing undocumented immigrants easy access to the country.
Host Brazil has invited the leaders of the 31 other nations that will compete in the World Cup to watch their teams play, which will add to security concerns. Brazilian authorities say the risk of a terrorist attack is low because Brazil has no enemies.
The Brazilian Air Force will enforce no-fly zones over the soccer stadiums during the 64 games that will be played between June 12 and July 13.
The most serious security threat will likely come from a repeat of street demonstrations by Brazilians who turned out in mass last year during a warm-up for the World Cup to protests against poor public services, corruption and the great expense of building the stadiums.