By Scott Malone

, (Reuters) - The 1.5 million people expected to pack into Philadelphia this fall for Pope Francis' first visit to the United States will fill the city's hotels, motels and Patricia Hughey's spare rooms.

Hughey and her husband are among the more than 1,000 Philadelphia-area households who have signed up to host visitors attending a September summit on families organized by the Roman Catholic church, which will come at the start of the week of Francis' visit to the United States.

"When I heard that the Pope was going to come, really my first thought was 'Oh my gosh, they are going to need hosts for this enormous crush of people'," said Hughey, who is 57 and said she was raised Catholic in Alabama but is no longer a member of the church.

For Hughey, who plans to host two brothers from the Democratic Republic of Congo and a married couple from Vietnam, a lot of the appeal was the chance to show off her adopted hometown and meet visitors from some of the 150 foreign delegations attending the World Meeting of Families. Visitors will pay host families a token fee to cover costs.

"We love to travel and I love meeting people from other countries," said Hughey. "Hosting somebody from a completely other country and culture is an opportunity that's a little hard to come by."

The Pope's visit to the "City of Brotherly Love," which will cap a week in which he speaks to the U.S. Congress and the United Nations, is expected to give Philadelphia's economy a $417.9 million boost, with much of the spending going to hotels and restaurants, according to the Philadelphia Convention and Visitors Bureau.

Organizers of the week-long meeting, that leads up to a Sept. 27 Mass expected to draw over 1.5 million people, said they asked area residents to offer space in their homes for visitors who might not be able to afford hotel stays.

Founded by Quakers in the late 17th century, Philadelphia gained a large Catholic population through immigration from traditionally Roman Catholic countries such as Italy and Ireland.

"We'll have young people coming who are willing to sleep on floors, families coming who are thrilled they will have some place to stay they can afford," said Donna Farrell, the meeting's executive director. "They will be viewing this as a pilgrimage."

Visitors who do not plan to stay with host families will have a hard time finding accommodation. With more than four months to go before Francis' visit, many major downtown Philadelphia hotels are already booked solid, according to travel reservation web sites.

Some 1,200 Philadelphia residents and families have already signed up through the Website at Homestay.com that meeting organizers are using to connect willing host families with potential guests, Farrell said.

Francis' visit comes at a time that Americans are drifting away from the Catholic church, according to a study by the Pew Research Center released on Tuesday.

About one in five U.S. adults, or 20.9 percent, identified as Catholic during the survey, a decline since the 2007 version of the study, which found 23.9 percent of adults said they were Catholic.

The decline reflects the fact that four out of ten people raised in the U.S. Catholic church have left the faith, with that decline partly offset by Catholic immigrants.

ACTIVE HOSTS

It is common for Americans to rent out their homes for events that draw large numbers of out-of-town visitors, such as the Masters golf tournament in Augusta, Georgia, or Mardis Gras celebrations in New Orleans. But many of the families looking for guests for the Pope's visit plan to remain in Philadelphia, spend time with their visitors, and are not in it for the money, according to Farrell and prospective hosts.

"It's going to make the experience more exciting to be sharing it," said Renee Bowen, 47, who has offered a room in the Wayne, Pennsylvania, home where she lives with her husband, 12-year-old twins and three cats. "I felt that it would enhance the experience."

The Homestay.com site used to connect host families with guests set a minimum fee of $50 per night, with the Web site collecting 10 percent of that. That compares with the $200 or more per night advertised by hotels at least 10 miles outside of Philadelphia that still have rooms available.

Some members of the city's immigrant community have also been signing up to host visitors, organizers said. Among them are many families in Philadelphia's St. Helena Parish, whose members include more than 200 families of Vietnamese origin and about 150 from Latin America.

The church's pastor, Monsignor Joseph Trinh, said parishioners had been lining up to host guests and offer translation services. Roughly 300 Vietnamese clergy and lay people have signed up to attend the meeting, the second-largest foreign delegation after Canada's, according to organizers.

"They feel honored to help because we have been welcomed here," said Trinh, who immigrated to the United States from Vietnam in 1975, after U.S. troops withdrew at the end of the Vietnam War.

"We know what it's like to have four or five people living in a room," said Trinh, who expects to feed about 120 Vietnamese visitors breakfast and dinner each day of the meeting. "They are willing to be a part of it, to give back some of what they have received here in Philadelphia."

(Reporting by Scott Malone in Boston, editing by Jill Serjeant and Andrew Hay)