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EMERGING MARKETS-Brazil stocks choppy ahead of Fed, Petrobras down

* Brazil Bovespa little changed * Mexico IPC down 0.4 pct SAO PAULO, Dec 17 (Reuters) - Brazilian stocks whipsawed on Tuesday with investors jittery a day ahead of the U.S. Federal Reserve's decision on whether to reduce its monetary stimulus program.

Mexico's IPC index fell for the third session in four, while Chile's bourse was little changed.

The Fed's bond-buying program has helped support global demand for riskier assets such as Latin American equities, but the Fed has repeatedly said that it will reduce the program's scale once it is confident the U.S. economic recovery is sustainable. The question for investors has been when the Fed will decide the time is right.

Investors have avoided taking big positions in local shares until after the Fed concludes its two-day policy meeting on Wednesday, the last of this year, and issues a decision on the program, analysts said.

Brazil's benchmark Bovespa stock index was little changed at 50,278.11 points after having swung widely earlier in the session.

Shares of state-run oil company Petroleo Brasileiro SA , known as Petrobras, fell for the first session in four, losing 2 percent and erasing the previous session's gains.

"Some analysts are saying there is a risk of the company defaulting in coming years," said Leandro Silvestrini, a broker with Intrader in Sao Paulo.

In October Moody's Investors Service downgraded Petrobras' debt rating on concern that fuel subsidies and huge investment commitments will cause its debt to grow until at least 2015.

Silvestrini said gains in Petrobras stock tend to be short-lived due to investor caution over government interference in the company, particularly on fuel price policy, which has led to deep losses in its refining division.

Shares of education firm Abril Educação SA fell 0.9 percent. Analysts at Banco Fator SA's brokerage unit initiated coverage of the firm with an "overweight" rating on Tuesday, citing good merger and acquisition opportunities and synergies from recent acquisitions.

Shares of toll road operator CCR SA rose 1.77 percent after the company won the rights on Tuesday to operate a stretch of highway in Brazil's soy belt.

Mexico's IPC index fell 0.4 percent to 41,886.02 points, a level it has not closed below since Nov. 26.

President Enrique Pena Nieto said on Monday he would soon enact a sweeping overhaul of Mexico's ailing energy sector that is aimed at boosting growth in Latin America's No. 2 economy. Signs of stronger growth and the initial effects of major economic reforms could help support Mexican equities next year, traders said in a recent poll.

Chile's IPSA index was little changed at 3,688.20 points as a 1.9 percent gain in shares of retailer Cencosud helped offset a 2.95 percent decline in Latam Airlines Group.

Latin America's key stock indexes at 1633 GMT: Stock indexes Latest daily % YTD % change change MSCI LatAm 3,179.64 -0.22 -16.09 Brazil Bovespa 50,278.11 0 -17.51 Mexico IPC 41,886.02 -0.4 -4.16 Chile IPSA 3,688.20 -0.01 -14.26 Chile IGPA 18,146.77 -0.18 -13.88 Argentina MerVal 5,332.10 -0.9 86.81 Colombia IGBC 13,037.19 -0.02 -11.41 Peru IGRA 15,607.06 0.4 -24.35 Venezuela IBC 2,654,958.12 -0.38 463.16