But despite the city’s connection to the East and Venice’s relatively tolerant attitude toward immigrants, contemporary Venetians have been wary about a more visible presence of Islam. A proposal by Qatar to help build a museum of Islamic art and history in a palazzo near the Rialto Bridge has been met with opposition, vocally so by the right-wing, anti-immigrant Northern League party, whose leader vowed to occupy the space proposed for the museum to prevent its construction.

Mr. Büchel, 48, is a famously combative artist who has specialized in hyper-real installations that often lay bare the art world’s hypocrisies and political contradictions (he once built a working community center, with classes for the elderly, inside an elegant London gallery). In an interview, he said he wanted a church to host the mosque in order to create a quintessentially Venetian layering of cultures. But he spent months with no luck trying to find a willing partner for “The Mosque: The First Mosque in the Historic City of Venice,” as the project is titled. He was finally able to rent a small Catholic church, Santa Maria della Misericordia, that has not been used for worship for more than 40 years and is now owned by a lighting company. But his real difficulties in creating the project began only then.

In meetings with Venetian leaders, the police and officials of the Biennale, Mr. Büchel was told that he would not be allowed to make temporary changes to the church’s exterior, including a bas-relief he had planned near the entrance that would have said “Allahu akbar” (or “God is great”) in Arabic script.