Mexico opposition holds lead in July election

MEXICO CITY (Reuters) - Mexico's opposition Institutional Revolutionary Party, or PRI, held a firm lead heading into congressional elections on July 5, according to a poll by Consulta Mitofsky published on Tuesday.

The centrist PRI, which ruled Mexico for most of the 20th century until its defeat by the National Action Party, or PAN, in 2000, is set to win 34 percent of the vote for the lower house of Congress, making it the biggest party in the chamber, according to the poll.

All the seats in the lower house are up for grabs.

President Felipe Calderon's PAN is seen picking up 29 percent of the vote while the leftist Democratic Revolutionary Party, or PRD, is seen winning just 13 percent.

Such an outcome would roughly double the number of seats the PRI holds in the lower house, giving it more than 210 seats out of 500, but shy of a simple majority, according to the poll, Mitofsky's last before Sunday's vote.

The PAN's representation will lose its position as the No. 1 party and could be cut to less than 177 seats, leaving it with around one-third or less of the seats in the house, the poll said.

The poll was carried out from June 25-28 by face-to-face interviews with 2,000 people and has a margin of error of 2.2 percent 95 percent of the time.

(Reporting by Michael O'Boyle, editing by Philip Barbara)