* Trade surplus of $437 million is biggest since March
* September imports down 1.44 percent in month
* Economists say data back bets for slower 2nd-half growth
MEXICO CITY, Oct 25 (Reuters) - Mexican imports slowed in September, allowing Latin America's number two economy to post its biggest trade surplus in six months but bolstering fears of slower growth. Imports fell 1.44 percent last month, weighed down by a slump in purchases of unfinished goods such as car parts. That pushed the trade surplus to a six-month high of $437 million , the biggest since March, the national statistics agency said on Thursday. September's figure handily beat August's surplus of $12.5 million, originally reported as a $175 million deficit. Total exports also fell, for the second month in a row, down 0.05 percent in seasonally adjusted terms. Manufacturing exports fell 0.33 percent, dragged down by a 0.8 percent fall in automotive exports. Cars have been a mainstay of Mexico's recent export gains, with Mexico now the fourth-biggest exporter of cars globally. The country has attracted new investment from companies including Audi, Mazda and Nissan.
But some economists, many of whom were already expecting slower growth in the second half of 2012, were unfazed by the drop in exports. ``The domestic side is keeping itself afloat and this has compensated for the drop (in exports),'' said Marco Oviedo, an economist at Barclays in Mexico. ``That's why we think the economy will keep slowing down but softly.'' Stripping out oil-related products, consumer imports rose 0.34 percent in September, a positive sign for domestic demand. But imports of unfinished goods such as vehicle components, which tend to predict future export levels, fell 1.76 percent. Mexico's economy grew an average 4.3 percent in annual terms in the first half of the year, but the finance ministry has predicted a slower expansion of 3.5 to 4.0 percent for 2012. Economic activity data for August released Wednesday backed those bets, with annual growth easing to 3.51 percent. In non-seasonally adjusted terms, Mexico posted a trade surplus of $234 million, against a $979 million deficit in August.