The lobbying effort was expected to get a boost on Thursday when U.S. President Barack Obama meets with Francis at the Vatican.
The governor of Pennsylvania, Tom Corbett, and Philadelphia Mayor Michael Nutter made their pitch to Archbishop Vincenzo Paglia, whose Pontifical Council for the Family is helping organize the Sept. 22-27 meeting.
Popes have attended five of the seven World Meetings of the Family, and Francis has made family issues the top priority of his pontificate. He also has a standing invitation to address the U.S. Congress and would presumably speak at the United Nations if he were on the East Coast.
But no confirmation of his participation is expected before next year.
Nutter said the celebration in Philadelphia offers Francis "a signature opportunity" to speak about family concerns to a huge audience.
"Francis' message needs to be heard in the United States," he said, giving Paglia a replica of the Liberty Bell.
The event will take place just before Francis convenes the second summit of the world's bishops to discuss such thorny family issues as contraception, gay marriage and allowing divorced and civilly remarried Catholics to receive Communion.
Paglia was asked at a press conference if families such as divorced Catholics might participate officially in the event, given that Francis himself has spoken of the difficulties faced by children growing up in non-traditional families.
Paglia said the Philadelphia meeting aimed to celebrate the "plurality" that both Philadelphia and the United States are known for.
"We can't deal with family issues in a corner or on the side," he said. "The debate that Pope Francis himself has asked for on these issues is a debate that is part of the life of the Catholic Church."
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