BRASILIA (Reuters) - Brazil's government authorized an emergency transfer of 2.9 billion reais ($850 million) on Tuesday for the cash-strapped state of Rio de Janeiro to help pay for infrastructure projects and security for the Olympic Games in August.

The authorization, published in the government's official gazette, confirmed a Reuters report on Saturday. The funds will be transferred to Rio once a supplementary credit is added to the budget, the gazette said.

Rio's financial crisis threatens to disrupt public services during the Olympics when 500,000 foreign visitors are expected to visit the beach-side city.

Rio de Janeiro acting Governor Francisco Dornelles declared a state of financial emergency on Friday as a drop in revenues caused by a crippling recession and slumping oil prices left state coffers depleted. The games start on Aug. 5.

The federal government was already considering an emergency loan to Rio after missing interest payments with multilateral banks in May. The missed payments complicated the release of a 1 billion-real loan from the state development bank BNDES to finish a subway line in the city of Rio de Janeiro.

(Reporting by Lisandra Paraguassú and Marcela Ayres; Writing by Anthony Boadle; Editing by Tom Brown and Cynthia Osterman)