By Mark Abrams

PHILADELPHIA (CBS) — Philadelphia archbishop Charles Chaput is leading the planning and is getting the support of local officials for the Vatican’s “World Families Conference,” coming to Philadelphia in September 2015 (see previous story).

It’s an event that is projected to draw tens of thousands of Catholics from around the world for the six-day event.

Archbishop Chaput — who had been asked by Pope Benedict XVI last summer in Milan, at the last World Meeting of Families, to host the next event — says it’s now official, with the dates set: September 22nd to 27th, 2015.

The pope had told Chaput he would come, but is now retiring at the end of the week.

What about the next pope making the journey?

“We’re going to plan as though he’s going to come,” Chaput said today.  “But we can’t promise because the man who’s going to be pope hasn’t been chosen yet and hasn’t committed himself.  So we can’t promise for somebody.”

Chaput says he’ll make a personal pitch when he travels to the Vatican sometime in the coming months for planning meetings.  He also says that Philadelphia mayor Michael Nutter and Pennsylvania governor Tom Corbett have agreed to be co-hosts for the event.

Nutter says there will be a significant economic impact from the conference, and he’s calling on the business community and civic leaders to get ready.

“Working together, we can elevate Philadelphia as one of the great international destinations of the world,” the mayor said today.

Nutter says he will work with the archbishop in private fundraising efforts to underwrite what could be a more-than-$10-million undertaking.