BANDA ACEH, Indonesia  Under Islamic law, or Shariah, the religious police have administered public canings for such things as gambling, prostitution and illicit affairs. But under a new Islamic criminal code that goes into effect this month, the Shariah police will be wielding a new and more potent threat: death by stoning for adulterers.

Most of Indonesia still lives up to its reputation for a moderate, easygoing brand of Islam, and Islamist parties suffered heavy losses in this year’s national elections. But how Aceh went from basic Islamic law to endorsing stoning in a few short years shows how a small, radical minority has successfully pushed its agenda, locally and nationally, by cowing political and religious moderates.

Though extreme, Aceh is not an isolated case. In recent years, as part of a decentralization of power away from the capital, Jakarta, at least 50 local governments have used their new authority to pass Shariah-based regulations regarding conduct and dress, though none have gone as far as Aceh to deal with criminal matters.

Most experts and human rights advocates believe the regulations discriminate against non-Muslim minorities and contravene the country’s Constitution, which guarantees freedom of religion. But the government of President Susilo Bambang Yudhoyono  a moderate former general whose Muslim credentials have often been questioned by political opponents  has not challenged them. In fact, Mr. Yudhoyono has backed morality-based laws that pleased Muslim conservative allies but angered advocates of human rights.