Early in the candidates' forum last night, U.S. Rep. Chaka Fattah expressed his hopes about how the Democratic race to be the next mayor of Philadelphia might unfold over the next three months.

"We deserve a campaign focused on substance," he said, "that doesn't get mired down in personalities and pettiness."

And for much of the evening, that's the kind of campaigning the five major candidates delivered, as they shared a stage for the first time.

With varying degrees of specificity and focus, they addressed the urban environmental issues that were supposed to be the subject of the evening. But there was a fair share of sniping and back-biting as well, most of it delivered with laughs and smiles.

For instance, businessman Tom Knox twice suggested that the three legislators in the race - Fattah, U.S. Rep. Bob Brady and state Rep. Dwight Evans - would best serve Philadelphia by keeping their current jobs.

"This should be a race between Michael and me," Knox said, referring to former City Councilman Michael A. Nutter.

"I can support that," Nutter replied. "If we do that, can you lend me a little money . . . at a lower rate."

That remark was a reference, seemingly understood by many of the 400 people in the auditorium of the Academy of Natural Sciences, both to Knox's personal wealth and to his having briefly headed a bank that engaged in the business of high-interest payday loans.

Evans, on two occasions, took on all four of his opponents on the question of credentials.

"All these are very nice people," he said at one point. "But the question is who is qualified to lead."

And the answer, he said, was Dwight Evans.

Brady, making his first appearance with the others as an announced candidate, reacted with mock horror to the verbal shots being taken.

"I might be shocked to find that I might be the most civil guy on the stage," he said.

For much of the evening, the candidates were asked to respond to a 10-point action plan issued last month by the Next Great City initiative, the forum's sponsor, which counts 76 civic and environmental groups among its backers. The plan is designed to help Philadelphia's next mayor and City Council make neighborhoods cleaner and healthier.

All five of the would-be mayors endorsed the full list of the group's recommendations, which are meant to be practical and low-cost.

Among the provisions are calls to put anti-pollution filters on old city trucks and buses; to replant 23,000 trees cut down by the city since 2001; and to make recycling easier for residents by letting them put all their recyclables into a single container.

In addition, all of the contenders made sure to emphasize the themes that are at the heart of their candidacies.

Fattah spoke of the need to create opportunities for the impoverished, Brady of his ability to bring people together.

Evans stressed the priority of public safety, Nutter his record in City Council, and Knox the need to end pay-to-play politics.

As even this event demonstrated, getting five candidates to show up at the same place at the same time is not easy. When the proceedings began, only Brady, Nutter and Knox were on stage. Fattah and Evans arrived a little later.

Numerous other groups have similar forums planned between now and May 15. Many will have to settle for less than perfect attendance, what with Brady and Fattah spending part of most weeks on Capitol Hill while another, Evans, has obligations in Harrisburg.

Contact senior writer Larry Eichel at 215-854-2415 or leichel@phillynews.com.