* Euro zone posts 900 mln euro surplus in January * Exports rise in southern Europe but fall in France BRUSSELS, March 18 (Reuters) - The euro zone's trade balance swung to a much smaller than expected surplus in January compared to a year ago, data showed on Tuesday, as imports fell and exports rose only modestly.
The 18 countries using the euro had an external trade surplus, unadjusted for seasonal swings, of 900 million euros ($1.25 billion) in January, well below economists' expectations for a surplus of 12 billion euros.
January's reading was still above the 5.4 billion euro deficit in the same month of last year, but was less impressive when compared with the 13.8 billion euro surplus in December.
Non-seasonally adjusted exports rose by 1 percent on the year in January after a 4 percent growth in December, while imports dropped 3 percent, following a 1 percent increase in December, the EU's statistics office Eurostat said.
On a seasonally adjusted basis, exports have been falling on a monthly basis since October. They accelerated the pace of decline to 1.3 percent in December from a 0.6 percent fall in November. Data for January is not yet available.
Data up to and including December includes the 17 countries using the euro, while data for January onwards includes Latvia, following its accession to the single currency.
The overall picture of export activity across the bloc remains mixed, with the southern periphery continuing to increase exports, led by Greece's 17.2 percent rise on the month, followed by Spain's 1.7 percent rise.
Germany, Europe's largest economy, saw exports rising month-on month in January by 1.2 percent. Exports from the euro zone's second largest economy France fell by 0.6 percent. Exports in Italy fell 0.2 percent in Italy in January.
Data for countries' January exports are seasonally adjusted.