SAN DIEGO (AP) — Whoever wins Tuesday's election for mayor of the nation's eighth-largest city will represent a break from the past.

A win by Councilman Carl DeMaio would make San Diego the largest U.S. city by far to choose an openly gay Republican leader. DeMaio also would become one of the few young Republicans elected to a high-profile office in California.

DeMaio, 38, made his political mark in the city by attacking municipal employee unions and attaching himself to the winning sides of ballot campaigns to privatize services, defeat a sales tax and cut public pensions.

U.S. Rep. Bob Filner has what looks like a golden opportunity for Democrats to capture an office that has eluded their grasp for most of four decades.

Filner, 70, is campaigning as a voice for those shut out of a City Hall that has long been led by moderate Republicans. The city's beleaguered labor unions have poured money into making him the city's first Democratic mayor since 1992.

Party affiliation favors Filner. Democrats overtook Republicans in voter registration in 1994 and now have a 12 percentage point edge. Still, several polls show a tight race.

DeMaio and Filner defeated two more moderate candidates in a June primary amid anemic turnout, leaving them to fight for voters in the middle. Each has sought to cast their opponent as polarizing and unaccustomed to compromise.

DeMaio won several endorsements from the city's business and political establishment, shedding some of his firebrand image. One prominent supporter is Irwin Jacobs, founder of San Diego-based technology bellwether Qualcomm Inc. and the second-largest donor to President Barack Obama's re-election campaign.

For Jacobs, the tipping point was Filner's theatrical presentation before the City Council in July to oppose Jacobs' plan to remake Balboa Park, home of the San Diego Zoo and other cultural jewels. Filner introduced an impersonator who played the part of a long-deceased park advocate and openly mused what would happen if the project's 79-year-old champion died.

"Bob went a little overboard," Jacobs said in an interview. "It was a much more emotional presentation (than DeMaio's). That kind of bothered me."

DeMaio has raised $3.3 million — compared to less than $1 million for Filner — and outside groups supporting the Republican's campaign have blanketed the airwaves.

One ad knocking Filner flashes a quote — "I'm a Congressman and can do whatever I want" — that was lifted from an immigration officer's report on a 2003 confrontation with Filner at a detention facility. Filner denies making the statement when he was trying to visit a constituent at the jail. Online newspaper Voice of San Diego interviewed a reporter who witnessed the encounter and didn't recall those words.

Another ad features an interview with a United Airlines baggage handler who had a run-in with Filner at Dulles International Airport in 2007. Filner pleaded guilty to a misdemeanor charge of trespassing.

When he was 18, Filner spent two months in a Mississippi jail in 1961 after joining the Freedom Riders in their civil rights campaign against segregation in the South.

"I got a tremendous optimism about change in America from that," he said. "We didn't make it perfect, but we changed it."

The Pittsburgh native was president of the San Diego school board during his first stint in elected office and chairman of the House Veterans Affairs Committee during his 10 terms in Congress.

As for criticism that he has a short fuse, he says, "I'm guilty of being passionate."

Filner calls DeMaio a "tea party Republican" who is cozy with developers. DeMaio's big financial backers include Douglas Manchester, a hotelier and conservative publisher of the city's dominant newspaper, U-T San Diego, whose editorial board has published two front-page endorsements of DeMaio.

DeMaio grew up in nearby Orange County, abandoned by his father two weeks before his mother died of cancer. Jesuits put him in boarding school and paid for more than seven years of education in the Washington area. After college, he created consulting firms that catered to governments and corporations, which he says he sold in 2007 for about $6 million.

DeMaio moved to San Diego in 2001, became a vocal critic of city leaders and employee unions when ill-conceived labor pacts came to light, and announced his bid for mayor during his first term on the City Council. He hitched his mayoral bid to a ballot measure to cut public pensions, which passed overwhelmingly in June.

DeMaio's sexual orientation has been a nonissue during the campaign. He supports gay marriage but was publicly silent on a 2008 state ballot measure to ban the practice and says gay issues won't be a priority for him as mayor.

"It presents an opportunity for me to be a role model," DeMaio said. "I understand that, I accept that, and my goal is to make this race and make my administration not about my orientation but about the ideas for creating jobs and fixing the city's finances."

Mayor Jerry Sanders, a popular former police chief who is being forced from office by term limits, has sometimes refused to mention DeMaio's name. He has castigated the councilman for his dire assessments of city finances and services and for taking undeserved credit for San Diego's fiscal turnaround.

"He probably takes credit for my weight loss, probably takes credit for the weeds I pulled in the backyard last week," Sanders has said.

When Sanders, who backed a losing candidate in the primary, appeared before television cameras last month to endorse DeMaio, he was pressed on their rocky history.

"Carl and I don't have lunch together. We're not in a bridge club together," he said