KABUL, Afghanistan – An Afghan man is being prosecuted in a Kabul court and could be sentenced to death on a charge of converting to Christianity from Islam, a crime under this country’s Islamic laws, a judge said yesterday.

The trial is believed to be the first of its kind in Afghanistan and highlights a struggle between religious conservatives and reformists over what shape Islam should take here four years after the ouster of the Islamic fundamentalist Taliban regime.

The defendant, 41-year-old Abdul Rahman, was arrested last month after his family accused him of becoming a Christian, Judge Ansarullah Mawlavezada told the Associated Press in an interview. Mr. Rahman was charged with rejecting Islam and his trial started Thursday.

During the one-day hearing, the defendant confessed that he converted to Christianity from Islam 16 years ago while working as a medical aid worker for an international Christian group helping Afghan refugees in the Pakistani city of Peshawar, Judge Mawlavezada said.

“We are not against any particular religion in the world. But in Afghanistan, this sort of thing is against the law,” the judge said. “It is an attack on Islam.”

Judge Mawlavezada said he would rule on the case within two months. Afghanistan’s constitution is based on Shariah law, which is interpreted by many Muslims to require that any Muslim who rejects Islam be sentenced to death, said Ahmad Fahim Hakim, deputy chairman of the state-sponsored Afghanistan Independent Human Rights Commission.

Repeated attempts to interview Mr. Rahman in detention were barred.

The prosecutor, Abdul Wasi, said he had offered to drop the charges if Mr. Rahman converted back to Islam, but he refused.

“He would have been forgiven if he changed back. But he said he was a Christian and would always remain one,” Mr. Wasi told AP. “We are Muslims and becoming a Christian is against our laws. He must get the death penalty.”

After being an aid worker for four years in Pakistan, Mr. Rahman moved to Germany for nine years, his father, Abdul Manan, said outside his Kabul home.

Mr. Rahman returned to Afghanistan in 2002 and tried to gain custody of his two daughters, now aged 13 and 14, who had been living with their grandparents their whole lives, the father said. A custody battle ensued and the matter was taken to the police.

During questioning, it emerged that Mr. Rahman was a Christian and was carrying a Bible. He was immediately arrested and charged, the father said.

Afghanistan is a conservative Islamic country. Some 99% of its 28 million people are Muslim, and the remainder are mainly Hindu.

A Christian aid worker in Kabul, who spoke on condition of anonymity because of the sensitivity of the matter, said there was no reliable figure for the number of Christians, though it was believed to be only in the dozens or low hundreds. He said few admit their faith because of fear of retribution and there are no known Afghan churches.

An old house in a war-wrecked suburb of Kabul serves as a Christian place of worship for expatriates. From the muddy street, the building looks like any other. Its guard, Abdul Wahid, said no Afghans go there.

The only other churches are believed to be inside foreign embassies or on bases belonging to the American-led coalition or a NATO peacekeeping force.

Mr. Hakim, the human rights advocate, said the case would attract widespread attention in Afghanistan and could be exploited by Muslim conservatives to rally opposition to reformists who are trying to moderate how the religion is practiced here.

“The reformists are trying to bring about positive changes,” he said. “This case could be fertile ground for extremists to manipulate things.”

Muslim clerics still hold considerable power in Afghanistan, especially in rural areas where most women wear all-encompassing burqas and are dominated by men.

Mr. Hakim said that if Mr. Rahman was acquitted, it would be a propaganda win for the Taliban rebels, who have stepped up their insurgency in the past year.

In the months before American-led troops ousted the Taliban in 2001, it claimed Western aid groups were trying to convert Afghan Muslims. They arrested eight foreign aid workers for allegedly preaching Christianity, but later released them unharmed.