San Francisco Public Defender Jeff Adachi declared himself a candidate for mayor on Friday, instantly redrawing the battle lines in the race around his controversial effort to overhaul the city’s pension system.

Adachi’s last-minute announcement, made less than an hour before the filing deadline for candidates, jolted San Francisco’s political circles just four days after interim Mayor Ed Lee’s decision to run for re-election upended what had been a low-wattage race.

If Lee’s candidacy injected polarizing personalities into the fray — he has been trailed incessantly by questions about his ties to former Mayor Willie L. Brown Jr. and Rose Pak, the powerful Chinatown consultant — then Adachi’s candidacy swept onto center stage the hottest political issue in town: pension reform.

“We have a huge fiscal crisis on our hands. Unless we take action, it’s going to get worse,” Adachi told reporters at City Hall just before 5 p.m. Friday. “The reforms that I have championed are reforms that are absolutely needed — along with action.”

For two consecutive years, Adachi has pushed for ballot initiatives to pare back public employee pension benefits, a crusade that has made him a loathed figure among labor unions and an outcast among the overwhelming majority of political leaders in the city.

In 2010, unions spent nearly $2 million and mobilized hundreds of workers to beat back Adachi's Proposition B with a campaign that portrayed the public defender as a “right wing” union-buster. This spring, Adachi put forward another proposition, informally known as “Son of B,” that would yield greater savings than a competing measure backed by the Lee administration and union leaders. 

At a mayoral forum Thursday night, all eight candidates onstage voiced their support for Lee’s pension proposal over Adachi’s. 

The public defender said Friday it was this week's debates that prompted him to make an 11th-hour entrance.

“It wasn’t until I really listened to what the candidates were saying that I realized that the candidates either don’t get it or they don’t want to get it,” Adachi said. “I want to make sure there’s a voice in there that’s talking about the fiscal reality of the city.”

When reporters reminded Adachi that he — like Lee earlier this week — entered the race after denying for months that he harbored any mayoral ambitions, Adachi shrugged.

"Maybe something's in the water," he said.

Even more so than Joanna Rees, the venture capitalist and political newcomer, and the relatively conservative Tony Hall, Adachi will represent the first truly viable outsider candidate.

In recent days candidates — most of whom are City Hall veterans — have questioned Lee's character to set themselves apart from the popular mayor, but, until Adachi, few contrasts in policy positions have emerged.

At the same time, Chris Lee, a San Francisco political consultant (no relation to the mayor), said Adachi could have furthered his pension reform campaign without inserting himself into the race.

“This is a bad way to get people talking about pensions,” he said. “It’s not about pensions and it’s all about Jeff. If he really cared about the issue, he’d be talking about the issue.”

When Lee unveiled his pension deal in May, he slammed Adachi for carrying forward with his solo effort and failing to compromise with labor.

“Our consensus approach here is the right thing to do,” Lee said, flanked by union leaders. “I leave Mr. Adachi to his viewpoint, but I’m sure that he has to recognize that this is the official city family and he doesn’t represent that.”

On Friday, Lee welcomed Adachi to the race.

“We look forward to hearing his ideas on creating jobs, keeping our streets safe and working together to get things done for San Francisco,” said Tony Winnicker, Lee’s campaign spokesman.

But labor leaders reacted with cynicism, accusing Adachi of using the pension reform issue over the past year as a “Trojan horse” for his mayoral ambitions.

Nathan Ballard, a Democratic strategist who is the spokesman for labor unions on pension reform issues, said Proposition B raised Adachi’s profile enough to make him a “viable candidate” for mayor, but also made him “a lightning rod for the animosity of labor unions.”

He painted Adachi as an extremist. “Many unions are feeling so betrayed that he is in the pocket of right-wing businessmen,” Ballard said.

Gary P. Delagnes, the head of the powerful police officers’ union, said he would refrain from attacking Adachi.

“I’m certainly not going to waste a dollar attacking the guy,” said Delagnes. “He’ll implode anyhow. He’s full of himself, an egomaniac.”

Adachi said he intended to abide by a $1.475 million spending cap that most other candidates have said they will honor voluntarily, but said he would not accept public financing. Lee is the only other major candidate who has declined public financing.

“How can we afford to spend millions of dollars at a time when our city faces hundreds of millions of dollars in deficits?” Adachi said.

When asked if he was prepared to tussle with labor — and other mayoral candidates — a year after the bruising battle over Prop. B, Adachi smiled, lifted both hands and gave the lapels on his pinstriped suit a nonchalant tug.

“If I was worried about being personally attacked,” he said, “I would stay at home.”