BRASILIA (Reuters) - Brazil's central government on Tuesday recorded its biggest primary budget deficit ever for the month of May, with revenues down and the economy stuck in a second year of recession.

The new Treasury chief Ana Paula Vescovi also said the Treasury will not authorize a credit line for Rio de Janeiro to conclude a metro line for the Olympics site until the state pays its debts with the federal government.

The central government account, which covers federal ministries, the central bank and social security, posted a primary budget deficit of 15.494 billion reais ($4.68 billion) for May, slightly better than the 17 billion reais shortfall expected by the market.

In April, the central government recorded a surplus of 9.751 billion reais.

Vescovi said the shortfall in May was in line with the government's expectations for a deficit of 170.5 billion reais in 2016. She said the government has no plans to change that annual deficit forecast and that will unveil its expectations for 2017 in coming weeks.

"This deficit goal does not allow for more spending... it uses realistic parameters in times of economic crisis," Vescovi said.

($1 = 3.3120 Brazilian reais)

(Reporting by Alonso Soto and Marcela Ayres; Editing by David Gregorio)