MEXICO CITY - The four candidates for Mexico's presidency officially launched their campaigns for the July 1 election on Friday, all of them promising change.

Enrique Pena Nieto, who is running for the Institutional Revolutionary Party that ruled Mexico from 1929 to 2000, used the word "change" 26 times in his first official campaign speech.

"Mexico is clear on what it wants, and it doesn't want more of the same," Pena Nieto declared in the western city of Guadalajara. "It wants to exit this stage of shadow and darkness and enter a new stage of light and hope."

Pena Nieto's focus on "a grand crusade for change" and "the change we want" echoed the 2008 campaign slogan of President Barack Obama, "change we can believe in." It was unclear whether that echo was intentional.

The Obama campaign's skilful use of social media in 2008, when it employed email, text messages and the Web to reach voters, appears to have made an impact on the Mexican political scene.

Josefina Vazquez Mota, whose pre-campaign appearances have been plagued by logistical difficulties and poor planning, told supporters Friday to use social media, "this new world that accompanies us," to attract potential voters.

"It's going to be hard to reach every corner of the country," Vazquez Mota acknowledged. In fact, the first female candidate for a major Mexican party has had trouble making it on time to campaign events in Mexico City, let alone the often violent and isolated outlying regions of the country.

Though she is an incumbent-party candidate, Vazquez Mota is campaigning on the one-word slogan, "Different," perhaps an attempt to distance herself from President Felipe Calderon's six-year offensive against drug cartels. More than 47,000 lives have been lost to drug-related violence in that time.

All three major-party candidates said they want to bring peace to Mexico.

Andres Manuel Lopez Obrador, who is making his second run for the presidency for the leftist Democratic Revolution Party after narrowly losing the 2006 election, said at his first campaign news conference Friday that he represents "true change."

Lopez Obrador led weeks of street blockades to protest what he claimed was fraud in the 2006 elections and later anointed himself as "legitimate president." He has since been seeking to change his angry, radical image for a softer one.

"Let all of us, from below, undertake a campaign to build a new, just, humane, dignified, free democratic and loving republic," he said.

Supporters such as 58-year-old schoolteacher Beatriz Lara Aguirre say Lopez Obrador has changed this time around: "He's more serene," she commented. But the leftist candidate complained as he did six years ago that "we are going to come up against money, government agencies and some news media who want to impose (the choice of) the next president on us."