The primary motive for the trip would be the eighth edition of the World Meeting of Families, an event held every three years that was launched under Pope John Paul II in 1994 and is held in various parts of the world.
The Vatican announced in February 2013, shortly before the resignation of Pope Benedict XVI, that the next edition will be Sept. 22-27, 2015, in Philadelphia.
The family has been a major preoccupation both for the church generally and for Francis personally. Among other things, the pope has dedicated the next meeting of the Synod of Bishops, scheduled for October, to the theme of the family.
Because the General Assembly of the United Nations generally meets in September, there is also speculation that Francis might combine the Philadelphia outing with a stop in New York to address the U.N.
Popes have not always attended previous versions of the World Meeting of Families, and there has been uncertainty ever since the election of Pope Francis whether he would make the trip.
As a rule, the Vatican does not confirm the dates of papal trips until shortly before they occur.
An official in the Philadelphia archdiocese told NCR on Friday that "these trips are never 'set' until they're official" and that church officials in Philadelphia have had "no official indication."
"We hope, but we don't know," he said.
If it happens, the trip would be noteworthy not just as Francis' first outing to the United States, but because of the context of a major Catholic event focused on the family.
Defense of the traditional family, defined as a union between a man and a woman and open to children, has been a major concern for the Catholic church both in the United States and in other parts of the world, especially in light of a growing push for legal recognition of same-sex marriage.
When Pope Francis met with French President François Hollande on Friday, for instance, a Vatican statement afterward said among other matters, the two men had discussed "the family" and "bioethical issues."
The Socialist Hollande signed a gay marriage law in May 2013 after backing it during the 2012 French elections.
Some Catholic lawmakers in various parts of the world have cited the pope's now-famous remark aboard the papal plane in July with regard to gays, "Who am I to judge?", to justify votes in favor of gay marriage.
A Maltese bishop, however, recently said after a meeting with Francis that the pope had reaffirmed a 2010 statement while he was still the archbishop of Buenos Aires, Argentina, that gay marriage represents an "anthropological regression."
In a September 2012 interview, Archbishop Charles Chaput of Philadelphia told NCR he was concerned the Meeting of Families might be seen as a massive rally against gay marriage.
"The enemies of the church's position will say that's what it is," Chaput said. "It's important for us not to let that happen."
Despite the risk, Chaput said in that September 2012 interview that a papal visit would be a boon for the church in Philadelphia.
"Everywhere I've been where the pope has gone, it's been a moment of grace for the local church," Chaput said.
"I experienced that in an extraordinary way in Denver, where I inherited a diocese that had hosted World Youth Day," he said, referring to the visit of Pope John Paul II in 1993. "That visit changed the face of Denver."
Privately, Vatican officials have expressed concern about a possible outing to the United States for a different reason: Francis is uncomfortable expressing himself in English. On the other hand, they note, that linguistic handicap has not prevented him from garnering high approval ratings among the country's Catholics and non-Catholics alike.
A late December CNN poll found that 88 percent of American Catholics have a favorable view of the pope, with the survey's director saying that Francis is "arguably the most well-regarded religious figure among the American public today."