UPDATE 1-Argentina March trade surplus expands 58 pct

(Updates with data on exports and imports)

BUENOS AIRES, April 29 (Reuters) - Argentina's March trade surplus expanded 58 percent from a year ago to $1.31 billion because of a steep year-on-year drop in imports as the economy slows, the government said on Wednesday.

March's exports fell 16 percent from a year earlier to $4.19 billion, while imports sank 31 percent to $2.89 billion.

The decline in exports was explained almost exclusively by lower prices, with fuel, grains and copper shipments taking the biggest hits.

The value of imports fell both because of a 25 percent drop in volume and an 8 percent decline in prices, the INDEC statistics agency said in a statement.

The importation of intermediate and capital goods fell the most sharply as Argentina's six-year economic boom grinds to a halt.

The government reported the trade surplus in the first quarter grew nearly 12 percent year-on-year to $3.56 billion. President Cristina Fernandez said last week the quarterly surplus had widened 6 percent to $3.40 billion.

The government revised its March 2008 trade surplus figure to $829 million from $819 million previously ARECI11. (Reporting by Lucas Bergman and Hilary Burke; Editing by Padraic Cassidy)