BOGOTA (Reuters) - The mayor of Colombia's capital Bogota is set to be ousted this month after losing a series of appeals against a decision to dismiss him for mismanagement in a case many see as symbolic of the country's polarized politics as a presidential vote nears.

Gustavo Petro, 53, Colombia's second-most powerful public official, is expected to be relieved of his duties later this month and banned from holding office for 15 years, as ordered by Inspector General Alejandro Ordonez in December over ill-fated changes the mayor tried to make to city waste collection operations.

The ouster of Petro, a former left-wing guerrilla, was confirmed on Tuesday after the Council of State, the highest authority judging cases involving government bodies, rejected his appeals, exhausting his options for recourse.

The sentence handed down in December by the right-wing Ordonez was widely perceived as disproportionate by many Bogotanos, prompting days of peaceful protest at a main city square by those who saw it as an attempt to marginalize the political left.

Colombia, with high levels of economic inequality, has been fighting a five-decade war with left-wing guerrillas who began seeking land reform for peasants before becoming involved in trafficking of cocaine. Left-wing politicians are often perceived as rebel sympathizers even thought many oppose violence.

The government has been engaged in peace talks with the FARC or Revolutionary Armed Forces of Colombia since November 2012 in Cuba's capital Havana, negotiations which have made slow but promising progress. Petro was a member of the now long-defunct M-19 guerrilla movement which disbanded to embrace politics.

Petro's ouster has widely been seen as proof in parts of Colombian society that there is little room for the left in the political establishment of a country where wealthy landowners and a small number of powerful families have long held huge sway.

The mayor is expected to step down within 10 days upon the signing of a decree by President Juan Manuel Santos after he has been formally notified of the Council's decision. Fifteen of its members voted in favor of maintaining Ordonez' sentence while eight voted against.

Santos will seek a second term in a presidential vote on May 25 which he says is critical to enable him to continue the peace process he has opened up with the FARC. The perception that a key public official was unfairly ousted under his watch could cost Santos some support at the polls.

Petro, Mayor since January 2012, said on his Twitter account that he would continue governing "until the end" and can still request that the decision be annulled, but sources close to the City Hall said he is almost certain not to do so.

(Reporting by Luis Jaime Acosta; Writing by Peter Murphy; Editing by Eric Walsh)