By Juan Montes 

MEXICO CITY -- Mexican leftist presidential candidate Andrés Manuel López Obrador, the front-runner ahead of July elections, would respect a renegotiated North American Free Trade Agreement if the U.S., Mexico and Canada reach a deal before the vote, according to a top aide.

Talks to redraw Nafta are at a critical point, with negotiators from the three countries in permanent session in Washington, D.C. Differences remain, particularly on how to increase regional content in the auto industry, but some observers say an agreement in principle could be reached in early May.

If a deal is sealed, a López Obrador administration wouldn't reopen the talks to renegotiate chapters already agreed on or seek to include new items, said Graciela Márquez, a Harvard-educated economist who has been named by Mr. López Obrador to become his economy minister if he wins the election. That would put Ms. Márquez in charge of trade and industry policies.

"We can't be renegotiating Nafta [permanently]," she said in an interview late Wednesday. Ms. Márquez said the new government would respect in principle the agreement, but would want to look carefully at the details.

Reopening the negotiation could cause financial turmoil and complicate the first months of a López Obrador government, which is seen by some businessmen with mistrust.

Quick implementation of an agreement would reduce economic uncertainty, Ms. Márquez said.

Mr. López Obrador says he is in favor of Nafta, although he notes that the export model Mexico adopted in the early 1980s has failed to bring about high rates of economic growth. The economy expanded an annual 2.3% on average in the past 35 years.

The 24-year-old trade pact is critical for Mexico, as exports -- the vast majority of them to the U.S. -- represent some 35% of Mexico's gross domestic product, according to government data.

But Mr. López Obrador says the export engine must be complemented with a boost to the domestic market through higher wages and more public investment. He seeks to make Mexico more self-sufficient in gasoline and agricultural products such as corn, which Mexico imports in large quantities from the U.S.

He has insisted that a Nafta agreement should include measures to lift Mexican workers' wages, agreeing on this point with the administration of U.S. President Donald Trump, which has proposed factoring wages in Nafta's auto content rules. The measure is seen with skepticism by the government of Mexican President Enrique Peña Nieto and is opposed by many in the Mexican private sector.

Ms. Márquez said that if wages aren't part of the trade agreement, Mr. López Obrador wouldn't insist on the issue as president, but would seek to lift wages through domestic policies.

Mr. López Obrador has a commanding lead ahead of the July 1 vote. A recent poll by the Reforma newspaper gave him a 22-point lead over second-placed Ricardo Anaya, the candidate of the conservative National Action Party.

If a deal on Nafta isn't reached before July and Mr. López Obrador wins the election, Ms. Márquez said she would ask to be kept informed about the negotiations during the transition period. Mexico's change of administration occurs on Dec. 1.

A López Obrador government would resume the negotiation where the previous government left off to strike a deal quickly, she added.

"Nafta is a state affair that goes beyond López Obrador or Peña Nieto," said Ms. Márquez. "It's about the future of the country."

Write to Juan Montes at juan.montes@wsj.com

(END) Dow Jones Newswires

April 26, 2018 14:33 ET (18:33 GMT)