March 23 (Bloomberg) -- U.S. Senate Majority Leader Bill Frist urged Secretary of State Condoleezza Rice to ``use every diplomatic means necessary'' to win the immediate release of an Afghan man facing the death penalty for converting from Islam to Christianity.

The case of Abdul Rahman is the first of its kind in Afghanistan since the U.S. in 2001 ousted the Taliban government, which imposed a strict interpretation of Islamic religious law.

Frist, a Tennessee Republican, described the charge against Rahman as ``ludicrous'' in a letter to Rice today. President George W. Bush yesterday called the case ``deeply troubling.''

The dispute over the prosecution of Rahman has exposed religious tensions in a country the Bush administration has promoted as a tolerant, emerging democracy. The U.S. is spending almost $1 billion a month on military operations and rebuilding in Afghanistan.

``It is fair to say that the United States has not spent the last four plus years liberating, defending, rebuilding and assisting Afghanistan's democratic development only to see the Afghani people remain subject to laws reminiscent of the Taliban's reign,'' Frist wrote to Rice.

A similar letter was sent to Afghanistan's ambassador to the U.S., Said Tayeb Jawad, Frist's office said.

Karzai Call

Rice today spoke by telephone with Afghanistan's President Hamid Karzai on the matter, White House spokesman Scott McClellan told reporters in Washington.

``She made very clear what our views were in the strongest possible terms,'' McClellan said. ``And she stressed the importance of Afghanistan finding a favorable resolution to this.''

Top Muslim clerics said today that Rahman, 41, should be executed, the Associated Press reported from Kabul. ``Rejecting Islam is insulting God. We will not allow God to be humiliated. This man must die,'' AP cited cleric Abdul Raoulf as saying. Raoulf was jailed three times by the Taliban, according to the news agency.

McClellan said the case ``clearly violates the universal freedoms that democracies around the world hold dear'' and noted that the Bush administration is watching the case ``very closely.''

Abdullah Abdullah, Afghanistan's foreign minister, faced sharp questions about the Rahman case today after he gave a speech at American University in Washington. One student asked why U.S. soldiers should protect Afghanistan if it can't guarantee freedom of religion.

`Security Interests'

``It is in the national security interests of Afghanistan to find a viable solution'' that will also preserve Afghan values, Abdullah said. He expressed confidence that ``a good solution'' would be found.

Afghanistan's constitution proclaims on the one hand that Islam is the state religion. On the other it says followers of other religions are free to exercise their faith.

Abdullah declined to elaborate on what he would consider a solution or outline possible ways in which the controversy might play out, saying ``it is a judicial process.''

The Afghan Embassy in Washington received ``hundreds'' of messages on the matter, Abdullah said earlier this week.

To contact the reporter on this story: Janine Zacharia in Washington at jzacharia@bloomberg.net Judy Mathewson in Washington at jmathewson@bloomberg.net.

Last Updated: March 23, 2006 15:21 EST