A "527" committee has surfaced in the Philadelphia mayor's race, and its goal is to torpedo front-runner Tom Knox.

A former city commissioner, Democrat Alex Z. Talmadge Jr., is the public face of a stealth political committee called Economic Justice Coalition for Truth.

Talmadge, who ran for district attorney in 2001, is listed as the so-called 527 committee's executive director in papers filed April 4 with the IRS. The documents say the group's purpose is "exploring the issues of economic justice as they relate to the business practices of Tom Knox, a man who now seeks the office of mayor."

In an interview last night, Talmadge said the group hoped to raise up to $200,000 for a television campaign.

"We're not close enough, but there's a lot of interest," Talmadge said. He declined to say how much has been collected so far - or from whom.

"We don't have to yet," he said. "These are organizations and individuals that don't want to be exposed."

Named for a section of the tax code that authorizes them, 527s can raise and spend unlimited amounts for political advocacy as long as they don't coordinate with any candidate.

Just such a committee, Swift Boat Veterans for Truth, savaged Democratic presidential nominee John Kerry's Vietnam War record in 2004, grievously wounding his campaign.

Under IRS rules, 527s must report donations over $200 and expenditures over $500 - but not right away. The filing deadline for Talmadge's committee is July 31, long after the May 15 Democratic mayoral primary.

Asked to voluntarily disclose his group's backers in order to better inform voters, Talmadge declined. "Good honest politics?" he said, laughing. "Those words don't often go together."

Knox, a businessman financing his own campaign, has been able to outspend four rivals bound by the city's contribution caps. He is leading in polls.

"There was a group of people who wanted to be able to tell the true business history of Tom Knox," Talmadge said last night.

Talmadge, a longtime Democrat, said he had not communicated with the campaign of U.S. Rep. Bob Brady - the party's city chairman - or any other mayoral campaign. The Brady camp, too, denied any involvement.

Word of the committee drew a sharp reaction last night from Knox campaign manager Josh Morrow. "These guys are going to hide behind this thin veil of 'independence' while trying to smear our guy," Morrow said. "This thing just stinks."