MILLIONAIRE mayoral candidate Tom Knox has dramatically increased his spending on television advertising, dumping $740,000 into broadcast ads this week. That's more than twice his previous buys and more than twice the level of any other candidate.

Knox's massive ad purchase yesterday came on the same day he pledged to limit his own spending on the race to "what I've put in so far," at a lively morning debate on KYW Newsradio.

The level of Knox's spending on the campaign won't be known until campaign-finance reports are filed Friday, but the businessman has lately become the target of negative ads from a newly formed committee with undisclosed contributors.

Knox, who leads in the polls, was the focus of much of yesterday's debate among the five leading Democratic candidates. At one point, he taunted his four opponents, all of whom have held elective office.

"They've got 74 years of experience [in office] and they're bragging about their experience," Knox said. "I judge results on performance, not experience. So let's see. Has crime gone down? Has jobs gotten better?"

U.S. Rep. Bob Brady retorted, "We've been helping working men and women, and those that want to be working men and women. Mr. Knox has been ripping off working men and women."

Brady was referring to Knox's experience with high-interest payday lending through Crusader Bank, which Knox owned in the late 1990s. Reporter Steve Tawa grilled Knox about that, and about fines in Maryland against his health-insurance company.

"Banks make loans," Knox said. "Less than 2 percent of our assets were invested into the predatory lending, or payday loans . . . we got out of it before every other bank got out of it. So we weren't in it."

"Do you regret it?" Tawa asked.

"At the time I think we made the right decision," Knox said. "I thought that people needed to be able to get small micro loans."

Knox denied that a Maryland health-insurance firm he once owned had ever "told people they had to get a doctor's permission to go to an emergency room."

"All they did was tell them that before going to an emergency room they should consider going to see their own doctor where they were better off," Knox said.

But state regulators fined the firm for a spring 2001 newsletter from Knox's company to policyholders reminding them to "call [their] Primary Care Physician for authorization prior to visiting an emergency room."

Knox said after the debate that the wording had been mistakenly inserted by someone in his firm.

REPORTER MIKE DUNN ASKED MICHAEL NUTTER WHETHER he'd undermined the Democratic Party and Philadelphia's independence when he became chairman of the Pennsylvania Convention Center after a 2002 takeover by Harrisburg Republicans.

"The Pennsylvania Convention Center was in trouble at the time," Nutter said. "It's not a position I sought. I was asked, and I think the responsible thing to do was to step up and serve . . . the center has turned around [and] business is coming back."

Nutter recently resigned to focus on his campaign.

U.S. Rep. Chaka Fattah emphasized his ambitious plan to attack poverty with proceeds from a long-term lease of the airport.

State Rep. Dwight Evans referred to his record as a leader in Harrisburg, saying he had built coalitions and had gotten results in education and other areas.

When the candidates were asked whom they would vote for if not themselves, only Knox offered a name: Evans, who's been last in most polls.

Late yesterday the Knox campaign unveiled a TV ad it will run to retaliate against a Washington, D.C.-based group called Working People for Truth, which is running ads attacking Knox.