UPDATE 2-Mexico oil output falls 7.8 pct in first quarter

* Output falls as giant Cantarell field drops 34 pct

* Higher production at Ku Maloob Zaap offsets some falls

* Exports decline nearly 26 percent (Updates throughout, adds byline)

By Robert Campbell

MEXICO CITY, April 21 (Reuters) - Mexican oil production fell 7.8 percent in the first quarter of 2009 to 2.667 million barrels per day as output from the aging Cantarell field slid further, state oil company Pemex said on Tuesday.

Mexico produced 2.652 million bpd in March, down 6.6 percent from the same month in 2008.

Cantarell, which has been losing about a third of its production capacity at annualized rates in recent months, produced 754,063 barrels per day in March, down 34 percent from a year ago.

Pemex has been struggling to contain the relentless decline of Cantarell, which produced more than 2 million bpd as recently as 2004.

The slide in output at Cantarell threatens Mexico's position as a major oil exporter and puts a key source of government revenues in jeopardy.