City voters were taking a major step toward ushering in a new political era.

Twelve candidates hoping to succeed longtime Mayor Thomas Menino were on the ballot in Tuesday's preliminary election, with only the top two vote-getters moving on to compete in the Nov. 5 final.

Menino announced earlier this year that he would retire after more than 20 years in office. The city's longest-serving mayor has battled a series of health problems in recent years.

The hopefuls are City Councilor Felix Arroyo; former school committee member John Barros; radio station owner Charles Clemons; Suffolk District Attorney Daniel Conley; City Councilor John Connolly; City Councilor Robert Consalvo; former state Rep. Charlotte Golar Richie; City Councilor Michael Ross; community organizer Bill Walczak; state Rep. Martin Walsh; former schoolteacher David Wyatt; and City Councilor Charles Yancey.

Success for any of the candidates in such a crowded field could well hinge on the ability of their campaigns to identify likely supporters and make sure those voters get to the polls.

It was estimated that roughly one-third of the city's more than 365,000 registered voters would cast ballots at 150 polling places throughout the city. Polling hours were 7 a.m. to 8 p.m.

Ballots will be printed in English and Spanish at all city precincts, and elections officials say Chinese and Vietnamese language ballots will also be available in certain precincts, with interpreters also on hand to assist voters.

In addition to the mayoral race, 19 candidates are vying for four at-large city council seats, with the top eight advancing to November's contest.