By Natalie Schachar

MEXICO CITY (Reuters) - Mexico's opposition conservatives would take back the presidency from the ruling Institutional Revolutionary Party, or PRI, if the next election, scheduled for 2018, were held now, according to a poll published on Wednesday.

The survey, conducted by Buendia & Laredo, found 24 percent of respondents would vote for the center-right National Action Party, or PAN, versus 20 percent who would opt for the PRI, led by President Enrique Pena Nieto. He is constitutionally barred from re-election.

The ruling party has been tarnished by a series of conflict-of-interest scandals embroiling Pena Nieto, his wife and finance minister, slower-than-expected economic growth, grisly drug violence and criticism he has failed to crack down on corruption.

The opinion poll comes about a month after the PAN and leftist allies routed the PRI in regional elections.

In third place in the poll was Morena, the left-leaning party of two-time presidential runner-up Andres Manuel Lopez Obrador, which had the support of 17 percent of respondents. Lopez Obrador's former party, the Party of the Democratic Revolution, or PRD, traditionally the main leftist force in Mexican politics, had just 6 percent support.

"The question is ... if PAN will manage to consolidate this support," said Jorge Buendia, head of the polling firm.

The PRI, which ruled Mexico for 71 consecutive years, was defeated by the PAN in 2000 and regained power when Pena Nieto was elected president in 2012.

The poll, based on 1,438 interviews, was conducted from June 24 to 28 and had a margin of error of 2.95 percentage points.

(Reporting by Natalie Schachar; Editing by Simon Gardner and Peter Cooney)