JERUSALEM -- Christians used to be a vital force in the Middle East. They dominated Lebanon and filled top jobs in the Palestinian movement. In Egypt, they were wealthy beyond their number. In Iraq, they packed the universities and professions. Across the region, their orientation was a vital link to the West, a counterpoint to prevailing trends.

But as Pope Benedict XVI wends his way across the Holy Land this week, he is addressing a dwindling and threatened Christian population driven to emigration by political violence, lack of economic opportunity and the rise of radical Islam. A region that a century ago was 20 percent Christian is about 5 percent today and dropping.

Since it was here that Jesus walked and Christianity was born, the papal visit highlights a prospect many consider deeply troubling for the globe's largest faith, adhered to by a third of humanity -- its most powerful and historic shrines could become museum relics with no connection to those who live among them.

"I fear the extinction of Christianity in Iraq and the Middle East," the Rev. Jean Benjamin Sleiman, the Catholic archbishop of Baghdad, said in a comment echoed across the region.

The pope, in a Mass on Tuesday at the foot of the Mount of Olives, addressed "the tragic reality" of the "departure of so many members of the Christian community in recent years."

He said: "While understandable reasons lead many, especially the young, to emigrate, this decision brings in its wake a great cultural and spiritual impoverishment to the city. Today I wish to repeat what I have said on other occasions: in the Holy Land there is room for everyone!"

On Sunday in Jordan the pope argued that Christians had a role here in reconciliation, that their very presence eased the strife, and that the decline of that presence could help to increase extremism. When the mix of beliefs and lifestyles goes down, orthodoxy rises, he said, as does uniformity of the cultural landscape in a region where tolerance is not an outstanding virtue.

A Syrian international aid worker said, "When other Arabs find out that I am Christian, many seem shocked to discover that you can be both an Arab and a Christian." The worker asked to remain anonymous so as not to bring attention to his faith.

The Middle East is now, of course, overwhelmingly Muslim. Except for Israel, with its six million Jews, there is no country where Islam does not prevail. This includes Lebanon, where Christians now amount to a quarter of the population, and the non-Arab countries of Iran and Turkey.

Local Christians are torn between sounding the alarm and staying mum, unsure whether attention will reduce the problem or aggravate it by driving out those who remain.

With Islam pushing aside nationalism as the central force behind the politics of identity, Christians who played important roles in various national struggles find themselves left out. And since Islamic culture, especially in its more fundamental stripes, often defines itself in contrast to the West, Christianity has in some places been relegated to an enemy -- or least foreign -- culture.

"Unless there is a turn toward secularism in the Arab world, I don't think there is a future for Christians here," said Sarkis Naoum, a Christian columnist for the Lebanese newspaper Al Nahar.

Just as some opponents of President Obama sought to defame him by claiming he was a Muslim, so in Turkey was President Abdullah Gul accused of having Christian origins. Mr. Gul won a court case last December against a member of Parliament who made the accusation.

A century ago there were millions of Christians in what is today Turkey; now there are 150,000. There is a house in Turkey where the Virgin Mary is believed to have spent her last days, yet the country's National Assembly and military have no Christian members or officers except temporary recruits doing mandatory service. Violence against Christians has risen.

Among Palestinians, Islam is also playing an unprecedented role in defining identity, especially in Gaza, ruled by Hamas. Benedict's arrival in Jerusalem on Monday prompted a radical member of the legislature in Gaza to call on Arab governments not to greet him because of his contentious remark in 2006 regarding the Prophet Muhammad.

The West Bank Palestinian leadership, more secular, tries to include Christians to ward off separatist sentiments and stop the population decline. It has been a losing battle. In 1948, Jerusalem was about one-fifth Christian. Today it is 2 percent.

Rafiq Husseini, the chief of staff of President Mahmoud Abbas's office, said of the exodus of Christians: "It is a very negative thing if it continues to happen. Our task, from the president downwards, is to keep the presence of the Christians alive and well."

In Bethlehem, where the Church of the Nativity marks where Jesus is said to have been born, Christians now make up barely a third of the population after centuries of being 80 percent of it. Emigration is the first option for anyone who has the opportunity, and there are large communities of Christian