(Adds comment that bank has no plans for more measures in paragraph 5)

By Walter Brandimarte and Alonso Soto

RIO DE JANEIRO/BRASILIA, July 25 (Reuters) - Brazil's central bank on Friday announced measures to inject as much as 45 billion reais ($20 billion) in credit into the country's ailing economy, which is weighed down by the highest borrowing costs in nearly three years.

The bank said it was freeing up an estimated 30 billion reais in the financial system through changes to banks' reserve requirements. An additional 15 billion reais may be unlocked "over time" by easing minimal capital requirements in credit operations, a central bank official said.

The move "aims at improving the distribution of liquidity in the economy" given a recent slowdown in credit and relatively low levels of loan defaults, the bank said in a statement.

After years of slow growth, the Brazilian economy is flirting with a recession as manufacturing shrinks and industry workers lose their jobs. Inflation, however, is running at 6.5 percent, the ceiling of a government target, leaving policymakers in a difficult position.

The bank has no plans for more measures to bolster credit, a senior government official told Reuters later on Friday.

Some economists said the measures were at odds with a central bank policy of holding interest rates high, thus keeping credit tighter, to fight inflation.

Just last week, the bank held its benchmark interest rate at 11 percent, the highest since October 2011. On Thursday, it made clear interest rates will not be cut any time soon.

"The Brazilian central bank has shown an amazing capacity for contradicting itself," said Jankiel Santos, chief economist with Espirito Santo Investment Bank. "It is hard to understand the reasoning behind the changes announced today that are intended to foster credit operations at a time when the Brazilian monetary authority tries to tame inflation."

But the new measures drew praise from local bankers.

"I see the measures in a positive way as they create conditions to increase credit in some financial market areas where liquidly was less loose," said Roberto Setubal, chief executive of Itaú Unibanco Holding SA, Brazil's largest private-sector bank.

President Dilma Rousseff's government has repeatedly accused private banks of being overly cautious when giving credit, increasing the burden for state-run banks.

The central bank later said in a statement that the new policies "do not change at all" its inflation projections.

Among the changes announced on Friday, banks will be allowed to use 50 percent of the amount they set aside as reserve requirements on term deposits to provide more credit or to purchase loan portfolios from eligible financial institutions.

In a separate statement, the central bank said it was easing minimum capital requirements for retail credit operations.

The decision aims at reviewing macroprudential measures that were implemented in 2010, when policymakers sought to slow down the pace of credit growth in Brazil.

Macroprudential policies are meant to care for the health of the financial system by changing reserve and capital requirements as well as, in the case of Brazil, taxing financial operations.

(Additional reporting by Patricia Duarte; Editing by W Simon and Mohammad Zargham)