UPDATE 2-Mexico April crude oil exports tumble -Pemex

(Recasts throughout and adds gas details, byline)

By Jason Lange

MEXICO CITY, May 23 (Reuters) - Mexico's oil exports fell sharply in April and production also slipped, putting pressure on the government to overhaul energy laws as the country's biggest oil field declines.

State oil company Pemex said on Friday that exports dropped to 1.439 million barrels per day during April, down nearly 12 percent from March levels. Exports this year through April are down 13 percent from the same period last year.

The April data comes as Mexico's left-wing opposition is holding up in Congress an oil reform proposal by conservative President Felipe Calderon aimed at increasing private sector involvement in oil to help boost exploration and production.

Mexico is the world's No. 6 producer of oil by volume and the No. 10 exporter, according to the U.S. Energy Information Administration, but years of underinvestment by past governments have left output and reserves declining.

Skyrocketing oil prices have more than cushioned the blow to federal finances, about one third of which come from Pemex taxes, but the decline in production is worrying for the United States, which depends on Mexico as one of its top oil suppliers.

Oil output fell in April to 2.767 million barrels per day, remaining below the firm's 3.0 million bpd target for the seventh straight month.

Average production over the first four months of the year is down 9 percent from the same period in 2007, Pemex said.