Five major candidates competed Tuesday in the Democratic primary for mayor, with a former city councilman hoping a recent surge in his popularity would help win a race focused on crime and corruption.

Michael Nutter, who gave up his council seat to run for mayor, took a lead in public opinion polls after spending months attacking two-term incumbent John Street, who is barred by term limits from running again.

The Democratic primary winner will be the overwhelming favorite in November. Nearly four of five city voters are Democrats, and the city has not elected a Republican mayor in nearly 60 years. Business leader Al Taubenberger was unopposed in the Republican primary.

A wild card could be a possible third run for office by former Republican Sam Katz, who has not ruled out seeking the mayor's office as an independent in the general election. Katz lost twice to Street.

Click here for FOXNews.com's State and Local Government center.

In the Democratic race, millionaire businessman Tom Knox's self-financed campaign got off to a fast start because of heavy advertising, but appeared to have faded.

The other candidates included U.S. Reps. Chaka Fattah and Bob Brady, a longtime behind-the-scenes political powerbroker in Philadelphia who struggled to attract voters, and state Rep. Dwight Evans.

Get-out-the-vote efforts were expected to be critical, with more than 20 percent of voters undecided going into the primary, according to surveys.

Voters have consistently called crime the most important issue in a city with more than 400 homicides last year, the most in nearly a decade. Slayings in 2007 are on pace to break last year's total.

The candidates offered a variety of anti-crime plans, including proposals for hiring hundreds more police officers. Nutter pushed one of the most controversial ideas — a police "stop-and-frisk" program in the most violent neighborhoods.

The candidates also spoke about the need to clean up City Hall in the wake of a corruption probe that became public when an FBI bug was found in Street's office a month before the 2003 election. Street was never charged, but the probe netted the convictions of nearly two dozen people, many with close ties to the mayor.

The racial makeup of the crowded field further muddied the electoral picture in a city with nearly equal numbers of black and white voters. Evans, Nutter and Fattah are black; Knox and Brady are white.

Click here for FOXNews.com's State and Local Government center.