UPDATE 3-Mexico ruling party losing Congress vote-exit polls

(For a TAKE A LOOK on Mexico, click [nN25302940])

* Calderon's National Action Party behind in exit polls

* Economy worries turn voters against government

* Opposition PRI party ahead (Recasts with exit poll results)

By Alistair Bell

MEXICO CITY, July 5 (Reuters) - Mexican President Felipe Calderon's party appeared headed for defeat in mid-term congressional elections on Sunday, frustrating his plans to implement reforms to heal the ailing economy.

Two separate exit polls showed Calderon's National Action Party, or PAN, with 29 percent of the vote, far behind the 40 percent for the opposition Institutional Revolutionary Party, or PRI.

The poor state of Mexico's economy, which is in deep recession due to the downturn in the United States next door, turned voters against Calderon, a dour conservative.

"Investment and exports are falling. It's a mess and it will be a long time before we recover," university professor Enrique Serrano, 51, said as he left a Mexico City polling station.