IF THERE'S a mystery in the 2007 mayor's race, it's the astonishing collapse of the campaign's original front-runner, U.S. Rep. Chaka Fattah.

"If you'd asked me six months ago, I would have bet the house Chaka Fattah would be the next mayor," said veteran Republican consultant Chris Mottola. "The idea that he couldn't have out-raised everyone and essentially sucked the oxygen out of the room is just stunning."

Fattah came in as a smart, seven-term congressman with racial crossover appeal.

Last year, he led the Democratic pack by 16 points, and held the lead in January, even after rival Tom Knox had spent millions on television.

But yesterday, he was battling for third place. What happened?

Fattah complained repeatedly in the campaign's closing days that he was mistreated by a biased news media.

"I think it's wonderful that the press wants Mr. Nutter to win, and I think it's great that you all are so enthusiastic about it," Fattah scolded at a news conference last week.

Last night, Fattah added that it was "a risk" to center his campaign on attacking poverty in the city.

But Fattah supporters and analysts point to other factors, most prominently Fattah's failure to raise enough money in the challenging environment of campaign-contribution limits.

"It begins and ends with money," said lawyer and Fattah supporter Alan Kessler. "I think he truly believed the courts would overturn the city's campaign-finance laws and allow him to make up ground very quickly in fundraising."

In past races, a front-runner would get big contributions from those seeking access to City Hall, whether he sought them or not. But with limits in place, candidates had to build broader fundraising bases.

It didn't help that Fattah had congressional duties to attend to, and many also pointed to the $10 million that Knox dumped into the race.

But Fattah was beaten by Nutter, who stuck to the campaign-finance limits earlier than anyone. Several supporters said Fattah simply failed to discipline himself as Nutter had to spend several hours a day making fundraising calls.

Supporters said there was confusion within Fattah's campaign staff about whether Fattah would be able to use money from his congressional-campaign account - stocked from fundraisers hosted by Bill Clinton and Barack Obama - for his mayoral run.

In the end, the congressional war chest was largely untapped.

Analyst Larry Ceisler said Fattah seemed to take the race for granted.

"He ran the race like a front-runner, and there was a sense of arrogance," Ceisler said.

And while Fattah brought a coherent program of attacking poverty, consultant Mottola said he somehow didn't connect with voters.

"His operating slogan seemed to be, 'I'm here, and aren't you lucky,' " Mottola said. "His words were right, but there was no oomph behind them. You couldn't hear the music."

Supporters said there were missteps, such as Fattah's clumsy handling of his refusal to release his income taxes, which became a prominent news story for several days.

"If we'd had enough money, that wouldn't have mattered," said one Fattah supporter who spoke on condition of anonymity. "But if you can't afford to get your message out [in TV ads], then these other things fill in the blanks."

Ceisler also said there was a fundamental error in strategy.

"His congressional district had a large number of white voters that he never really played to," Ceisler said. "They would have been his before Nutter's. But in his ads and his rhetoric, he wrote off the white vote."

When Nutter surged in April, Fattah lacked the money to match Nutter's TV buys, which only compounded Fattah's fundraising problems. Soon Nutter led the field and began picking up anti-Knox votes.

Ceisler said Fattah underestimated the challenge of a mayor's race.

"I always felt his early lead wasn't that real, that it was based on name recognition, including his wife's," Ceisler said, referring to TV news anchor Renee Chenault-Fattah. "When people really started examining the candidates, instead of building on it, he blew the advantage." *