MEXICO CITY (Reuters) - Mexico s finance minister resigned on Monday to seek the 2018 presidential nomination of the ruling party, anticipating a major break with tradition as it seeks outside help to clean up its tarnished image and stay in office for another six years. Jose Antonio Meade had been widely expected to run for the centrist Institutional Revolutionary Party (PRI), whose credibility has been seriously undermined by corruption scandals, gang violence and accusations of electoral fraud. Meade is not a PRI member, and his reputation for honesty has persuaded many party grandees that he is the best bet to take on the front-runner in the July 2018 presidential race, the leftist former mayor of Mexico City, Andres Manuel Lopez Obrador. PRI hopefuls can register from Dec. 3, and early indications suggested Meade would not face any major challengers. The PRI will formally elect its candidate on Feb. 18. He was warmly received by party members on a whistle-stop tour of organizations affiliated to the PRI in Mexico City on Monday. All the other early PRI favorites for the presidency expressed their support for him on Twitter. Soft-spoken and measured in tone, Meade, 48 first entered the Cabinet under the previous center-right administration of the National Action Party, or PAN. His ability to draw votes from other parties is viewed as one of his principal assets.  He ll be an attractive candidate for those who don t necessarily support the PRI,  tweeted Daniel Karam, who headed the Mexican Social Security Institute during Meade s initial Cabinet stint under the PAN. Eager to mend its reputation, the PRI changed its statutes in August to make it easier for outsiders to run for the job the party has held for most of the past century. At an event at his official residence, President Enrique Pena Nieto said Harvard-educated former World Bank official Jose Antonio Gonzalez Anaya would leave his job as chief executive of state oil company Pemex to replace Meade in the Finance Ministry. In a brief address at the ministry afterward, Meade said he would run for the presidency  after 20 years of serving my country continuously with integrity and honesty.  Lopez Obrador, twice runner-up for the presidency, has railed relentlessly for years against government graft. He quickly lashed out on Twitter against the PRI as  corrupt  and  predictable  after Meade made his announcement. Meade remains unknown to much of the Mexican public, and in opinion polls he lags far behind the veteran Lopez Obrador, who has sought to characterize all of the main opposition parties as corrupt extensions of the PRI. Serving as energy, then finance minister in 2011, Meade became foreign minister when Pena Nieto took office in December 2012. He later switched to the Social Development Ministry before returning to the Finance Ministry last year. Seen by allies as a discreet and diplomatic official, Meade s grasp of finance and economics is matched by few in Mexico, and his academic career includes degrees in law and economics as well as an economics doctorate from Yale. Crucially, argue his supporters, he has avoided the damaging scandals that have engulfed the PRI under Pena Nieto, who cannot constitutionally seek a second six-year term.       I thank (Meade) for his dedication and commitment and I wish him success in the project he has decided to undertake,  Pena Nieto said at the event at his Los Pinos residence. TV images showed Meade driving toward Los Pinos behind the wheel of a modest compact car, a frequent prop among Mexican politicians seeking to project the common touch. Gonzalez Anaya, who is related by marriage to influential former President Carlos Salinas de Gortari, will be replaced at Pemex by Carlos Trevino, a senior executive at the company. 