By Alexandra Ulmer

SANTIAGO (Reuters) - Former Chilean President Michelle Bachelet ended months of speculation late on Wednesday by announcing she will run in a November presidential election that she is favored to win.

A popular center-leftist who ruled the copper-exporting nation from 2006 to 2010, Bachelet will likely face a candidate from the right-wing bloc of President Sebastian Pinera, who is barred from seeking a consecutive term under the constitution.

Front-runners for the ruling coalition's candidacy are charismatic businessman and former Public Works Minister Laurence Golborne and former Defense Minister Andres Allamand, a seasoned politician.

"I've taken some time to think about this decision ... And with happiness, with determination and much humility, I've taken the decision to be a (presidential) candidate," Bachelet said to cheers during a speech in Santiago, days after she quit her job as the head of U.N. Women.

Bachelet's return after months of speculation is a great relief to her fractured left-wing coalition, which Pinera ousted from a 20-year rule. She is expected to face little competition in the primaries.

Bachelet, a pediatrician-turned-politician, was one of Chile's most popular presidents.

Voters liked her affable manner, welfare policies and credited her for solid economic growth in one of Latin America's most stable, business-friendly countries.

Her high-profile U.N. post and time away from local politics have boosted her popularity, political analysts say, and opinion polls show her with a wide lead over other potential candidates.

In a poll published in January by local pollster CEP, 49 percent of those surveyed said they wanted Bachelet to be Chile's next president, versus 11 percent for Golborne and 5 percent for Allamand.

But analysts warn Bachelet's large lead will likely ebb during what looks set to be a heated campaign.

Whoever is elected on November 17 or in a potential run-off on December 15 will face demands for improved distribution of a mining bonanza in the world's No. 1 copper producer.

While Chile's economy grew a robust 5.6 percent last year and unemployment is at a six-year low, the country has the steepest income inequality among Organization for Economic Cooperation and Development states.

Bachelet on Wednesday centered her speech on combating inequality, saying deep reforms were needed for Chile to become a developed country. Education, energy policy and wages are key electoral issues.

Chile's open economy and its solid institutions are expected to remain broadly intact regardless of who governs until 2018.

A single mother of three and a victim of torture under Augusto Pinochet's dictatorship, Bachelet was one of conservative Chile's most unusual leaders since the return to democracy in 1990.

Critics said too much of her appeal was based on personality. Others in the wide-ranging leftist bloc blasted her for not pushing through bolder social reforms.

Bachelet's legacy was tainted by a slow response on providing aid and halting looting after a devastating 8.8-magnitude earthquake hit at the end of her term in February 2010.

She faced sharp criticism over the failure of the navy's catastrophe-alert system to warn of the ensuing tsunami, leaving hundreds who survived the quake to be engulfed by huge waves that followed.

(Writing by Alexandra Ulmer; Editing by Helen Popper and Stacey Joyce)