(Adds comments by PM, commission, updates crown)
By Peter Laca and Marcin Grajewski
BRATISLAVA/BRUSSELS, April 16 (Reuters) - Slovakia passed the inflation test for adopting the euro in March, leaving an uncertain outlook for future price growth as the single big obstacle in its bid to join the euro area next year.
The 12-month average inflation was 2.2 percent in March, comfortably below the permitted ceiling of 3.2 percent, figures from European Union statistics office Eurostat showed on Wednesday.
The European Commission will say on May 7 whether Slovakia, a European Union member since 2004, can adopt the currency now shared by 15 nations.
Before making a final decision, it will use economic forecasts to be issued on April 28 to see if Slovakia is likely to keep inflation low into the future.
"In view of the inflation figure, indeed, it is below the reference value, but according to the treaty we must assess not just whether it is below the reference value but if it is below that value in a sustainable way," Commission spokeswoman Amelia Torres said.
Inflation calculated by European Union methodology was 0.3 percent on the month, raising the annual rate to 3.6 percent, the highest since December 2006, from 3.4 percent in February.
The year-on-year figure exactly matched inflation in the euro zone, which was revised up from a preliminary reading of 3.5 percent. Slovak Prime Minister Robert Fico said the inflation criterion ceiling was rising faster than actual inflation in the central European country.
"Today there is no reason to doubt that the Slovak Republic would be able to secure good state of public finances but also the rate of inflation in the upcoming period," he said.
FIXED CURRENCY, HIGHER INFLATION
The worries over the inflation outlook stem from the fact that many poorer EU countries catching up with the core of the euro zone have been able to keep prices low with the help of appreciating currencies which cut costs of imported goods.
Countries that have fixed their currencies removed this channel of real convergence with the euro zone and have seen their inflation rise, such as the Baltic states and new euro zone member Slovenia.
The sustainability of low inflation is considered a necessary condition for euro adoption, because policymakers have very limited room to correct price swings when they give up their independent monetary policy.
"The key debate will include the impact of the strengthening Slovak crown against the euro on inflation," said Jaromir Sindel, economist at Citibank in Prague.
"The European Central Bank might turn slightly negative because of this, but it has only an advisory role ... I think the politics (supporting Slovak entry) will prevail," he said.
Sindel added that Slovakia, whose economy soared by 10.4 percent last year, should revalue the crown currency's parity rate to the euro, now at 35.4424, prior to fixing the crown irrevocably to the euro to limit the inflation pressure.
The crown currency dipped to 32.360 by 1200 GMT <EURSKK=> from 32.290 ahead of the release, but still outperformed other currencies in central Europe.
The EU has urged Slovakia to tighten fiscal policy to counter price pressures that may arise after the country gives up its independent monetary policy.
The government cut the ceiling for the 2008 public finance deficit and set a more ambitious fiscal plan for 2009-2011. For Eurostat report, click on.................. [
] For Slovak CPI table, click on................. [ ] For Slovak INSTANT VIEW, click on.............. [ ] For euro zone inflation table, click on........ [ ] For Slovak PM Fico comments, click on.......... [ ] For Commission comments, click on.............. [ ] For Slovak c.bank comments, click on........... [ ] (Additional reporting by Martin Santa in Bratislava; writing by Peter Laca and Jan Lopatka; editing by Stephen Nisbet/David Christian-Edwards)