Two hired gunmen shot six bullets into the 74-year-old missionary on Saturday at a settlement of landless peasants 33 miles (50 km) from this town in northern Brazil's Para state.
A native of Dayton, Ohio, Stang was murdered despite constant warnings to authorities she faced death threats.
Some 930 miles (1,500 km) south of Anapu, government ministers held an emergency meeting in the capital Brasilia on violence in areas of Para like Anapu county - fast becoming known as Brazil's "Gaza strip".
The government pledged 2,000 troops as well as air force and police units for Para - an area twice the size of France, which has Brazil's highest number of land conflict deaths.
President Luiz Inacio Lula da Silva ordered the action after an outcry by international human rights groups at Stang's murder and US pressure to find her killers.
Land activists attending Stang's funeral found that hard to stomach. They have watched hundreds of rural workers and activists murdered without any action taken.
Police said another landless leader was murdered in Para state on Tuesday. Daniel Soares da Costa, head of a settlement in south-east Para, was shot dead by gunmen - the fourth rural killing in Para in as many days.
"Sister Dorothy, she is a North American, a nun, so there is massive reaction, and that hurts us very deeply," said Xavier Gilles, a Roman Catholic human rights worker.
Stang is the most prominent Amazon rights activist to be murdered since Chico Mendes was gunned down in 1988 defending rubber tappers in the world's largest forest.
The killing has drawn attention to lawlessness in regions like Anapu, an area the size of Wales, where guns are used to acquire land and hold onto it.
Lula's ambitious land settlement plans have inadvertently fanned the violence. He has promised land to 400,000 poor families to shrink income inequalities.