ROME — As its corporate sponsors continue to feel the pinch of the financial crisis, the Vatican has taken an unprecedented step and is appealing directly to tourists and collectors to help finance the restoration of Bernini’s 17th-century colonnade in St. Peter’s Square by buying limited edition stamps.

The Vatican’s Philatelic and Numismatic Office is offering a souvenir sheet of two 10-euro stamps that could raise 3 million euros for the project, if all 150,000 are sold.

“Fund-raising wasn’t going very well,” said the office’s director, Mauro Olivieri, who came up with the idea for the stamps this year after officials in various Vatican departments were invited to suggest initiatives to help pay for the colonnade’s restoration. The cleanup began in 2009 and was expected to take four years, but the work began to lag when funds dwindled....