JAKARTA, Indonesia, Dec. 25 - The men in the mosque looked up in surprise as a mob in white robes and white caps splashed down the muddy alley, waving long wooden batons and shouting, "God is great!"
Behind them, angry residents were throwing stones. But the running men had already done their work. Whacking their sticks, they had knocked down a makeshift outdoor gambling shop, sending plastic chairs and plywood tables tumbling across the nearby railroad tracks.
"Smash it!" they had shouted, dancing about in the dark. "Destroy the gambling dens!"
These are the new kids on the block - the most vocal of a crop of recently formed radical Islamic groups that are trying to shove their way onto Indonesia's political stage. They call themselves Defenders of Islam and they are out to eliminate the vices of drink, gambling and good times here in one of the most laissez- faire Muslim nations.
"I disagree with everything they're doing," said Susilo, one of the men in the mosque. "O.K., maybe gambling is wrong, but what they are doing is wrong too. It's just too rude."
But groups like the Defenders of Islam cannot be dismissed. Against the grain of a national culture that is overwhelmingly tolerant and inclusive, they have proliferated - noisily and sometimes violently - since the former dictator Suharto was forced from power in May 1998.
These groups are part of the tumult of the country's new openness – an awkward political adolescence that includes a wild and freewheeling press, squabbling political parties, restless separatist movements, assertive new pressure groups and a divided and unhappy military - making Indonesia a place of turmoil and uncertainty.
Amid half a dozen rebellions percolating in various regions of the archipelago, communal wars in Sulawesi and the Maluku islands have involved the bloodiest clashes between Muslims and Christians.
In addition, a long-running separatist war in Aceh is being fought in part in the name of Islam; Aceh is one of the most orthodox Muslim provinces. The separatist rebels in the Free Aceh Movement first rose up in the 1970's, and are as interested in controlling the province's rich oil and natural gas fields as they are in Islamic extremism.
But the revolt is brutal - at least 1,200 people have died in Aceh this year - and religion is one way of fomenting discontent against both Indonesian authorities and the ExxonMobil affiliate that runs the gas fields.
After years of bloodshed, revenge drives Aceh's war, and residents fear both sides.
"Every day, you have to read the situation and adjust your behavior," said a university professor in Aceh whose rector was recently killed by unknown gunmen. "Sometimes there is a telephone call with no one at the other end. I'm trying to be philosophical and keep my balance, but it's very hard."
Officials in Aceh are seeking to impose a limited form of Islamic law under a new autonomy arrangement. The resource-rich province is one that the central government cannot afford to let go, as it did rebellious East Timor, and it seems prepared to offer a sop to the Islamists to preserve control.
Indonesia is a country founded on the idea of secular government, and whether any of the more violent Islamic groups will have lasting impact is an open question. For now, they are more often political cudgels, almost always existing on the fringe.
Even in post-Suharto Indonesia, the most populous Muslim nation, with 210 million people, politics drives the ebb and flow of religion more forcefully than religion drives politics. Democracy and Islam do coexist, religions largely flourish side by side, alcohol is permitted and women have the same rights as men.
"The tolerance of religious pluralism is part of Indonesia's own long history," said John Bresnan, an expert on Indonesia at Columbia University. "This is one aspect of Indonesian Islam that is very notable."
Islam was mostly introduced here by traders, rather than imposed by conquerors. In the 700 years since, it has mingled and coexisted with local religions and in some forms, even today, Islam throbs with the magic and mysticism of the traditional culture of Java.
One of Islam's later landfalls is in Semarang, in central Java, where it was introduced in the early 15th century by a Chinese admiral, Cheng Ho, a convert. Today, a Buddhist shrine honors the admiral, and even devout Muslims come to light sticks of incense and pray to him for good fortune.
For all that, churches and mosques are periodically bombed in regions where forced resettlement under Mr. Suharto often created a potent mix of ethnic and religious hatred. A recently formed Islamic group has mobilized hundreds of fighters to travel to two remote areas where Muslims and Christians are fighting.
The group, Laskar Jihad, seems to operate with impunity and is believed to be backed by factions of the military and possibly by troublemakers from the former Suharto clique who continue to seek to destabilize the country.
Three years of killing have cost perhaps 5,000 lives on the Maluku islands, one of the Islamic fighters' targets. Religious leaders have been meeting this month to try to end a similar surge in violence in Sulawesi that has taken hundreds of lives and caused thousands of Christians to flee their homes.
American and other diplomats mostly play down any possible connections with Osama bin Laden or Al Qaeda, but they do note that terrorists on the run could find a haven here. In the longer term, diplomats say, violent Islamic groups could pose a greater danger if general instability increased.
The bedrock of Islam here, however, is still a pair of broadly based organizations, Muhammadiyah and Nahdlatul Ulama, which claim a membership of about one-fourth of Indonesians. Both are moderate in philosophy and have preserved the clear boundary between religion and politics mandated under Mr. Suharto and his predecessors in Indonesia's 52 years of independence.
In his 32 years in office, Mr. Suharto used force to suppress Islamic groups and control religious influence. But when he felt his power challenged more than a decade ago, he found tactical advantage in promoting Islam – the religion professed by 90 percent of Indonesians - encouraging some of its organizations and ostentatiously making the Muslim pilgrimage to Mecca.