TUNIS  The Tunisian revolution that overthrew decades of authoritarian rule has entered a delicate new phase in recent days over the role of Islam in politics. Tensions mounted here last week when military helicopters and security forces were called in to carry out an unusual mission: protecting the city’s brothels from a mob of zealots.

Police officers dispersed a group of rock-throwing protesters who streamed into a warren of alleyways lined with legally sanctioned bordellos shouting, “God is great!” and “No to brothels in a Muslim country!”

Five weeks after protesters forced out the country’s dictator, President Zine el-Abidine Ben Ali, Tunisians are locked in a fierce and noisy debate about how far, or even whether, Islamism should be infused into the new government.

About 98 percent of the population of 10 million is Muslim, but Tunisia’s liberal social policies and Western lifestyle shatter stereotypes of the Arab world. Abortion is legal, polygamy is banned and women commonly wear bikinis on the country’s Mediterranean beaches. Wine is openly sold in supermarkets and imbibed at bars across the country.