PHILADELPHIA (REUTERS) - The tiny black Fiat 500L that ferried Pope Francis to the White House and Congress during his historic first visit to the United States will be auctioned in Philadelphia next week, officials said on Wednesday.

The car, which the 79-year-old Pontiff chose as a symbol of his concern for the environment and desire to put aside some of the rich trappings long associated with his office, will be auctioned off on Jan 29, said organisers of last year's World Meeting of Families in Philadelphia.

Proceeds from the sale will benefit the Roman Catholic Archdiocese of Philadelphia, organizers said. The car will then go on display at the Philadelphia Auto Show, officials said.

The Fiat was one of two vehicles the Argentina-born Pontiff used during his visit to the Washington, New York and Philadelphia. The other was a white Jeep with open sides known as a "Popemobile" that allowed Francis to kiss babies as he passed.

Amid heavy security and typically surrounded by the large, armoured black limousines and SUVs preferred by travelling American politicians, the Fiat was conspicuous for its small size and ever-open rear window from which the Pope waved to crowds.

Thousands of Americans, both followers of the Catholic religion and the curious, packed into the streets of the three cities during Francis' September visit, during which he also addressed the United Nations and met with prisoners and homeless people.