KUWAIT/DUBAI (Reuters) - Every Friday in the Muslim Gulf Arab state of Kuwait, 2,000 Christians cram into a 600-seat church or listen outside to the mass relayed on loudspeakers, prompting their Catholic bishop to worry about a stampede.
"If a panic happens, it will be a catastrophe ... it is a miracle that nothing has happened," said Bishop Camillo Ballin.
These churchgoers represent only the tip of the iceberg. Ballin reckons his flock in Kuwait numbers around 350,000 out of a total of half a million Christians in the country.
At least 3.5 million Christians of all denominations live in the Gulf Arab region, the birthplace of Islam and home to some of the most conservative Arab Muslim societies in the world.
The freedom to practise Christianity -- or any religion other than Islam -- is not always a given in the Gulf and varies from country to country. Saudi Arabia, which applies an austere form of Sunni Islam, has by far the tightest restrictions.
"In the Gulf, excluding Saudi Arabia, government attitudes are more religious tolerance than religious freedom," said Bill Schwartz, canon of the Church of the Epiphany in Doha, Qatar, an Anglican church serving Protestants of various denominations.
Christians in the Gulf are almost all expatriate workers, mostly Catholics from the Philippines and India.
Christian leaders fret that their ability to worship is often compromised by lack of access or space, an issue they will raise at the Vatican next week during a synod of bishops called to discuss the fate of Christian minorities in the Middle East.
The welfare of Christians in Saudi Arabia, the world's top oil exporter and a close U.S. ally, is a pressing issue for church leaders, but progress is slow as the Saudi monarchy tussles with its powerful religious establishment over reforms.
Almost all the kingdom's clerics follow the strict Wahhabi school of Islam, and some believe non-Muslims should be barred from the Arabian peninsula, a view shared by al Qaeda which has threatened attacks against Christians in the region.
In Saudi Arabia, home to Islam's holiest sites, any form of non-Muslim worship takes place in private. Converting Muslims is punishable by death, although such sentences are rare.
Services and prayer meetings are often held in diplomats' homes, but access to these is very limited, so Christians meet to worship in hotel conference rooms -- at great risk.
This week, Saudi media said 13 Filipinos had been charged with proselytising after a raid on a Riyadh hotel where nearly 150 people had been attending a private Roman Catholic mass.
Diplomats say priests regularly visit Christians in Saudi Arabia. Even though their visas do not state their purpose, the authorities are aware of their presence.
The Catholic Church, which estimates it has 1.5 million adherents in Saudi Arabia, has urged Riyadh to lift curbs on Christian worship and allow churches to be built, just as Muslims can build mosques in Western countries.
The pace of change may be glacial, but Christians and rights activists note some improvements as the kingdom slowly opens up to the world and heeds international pressure on human rights.
"Ten years ago a Saudi who said he was a Christian would have had his head cut off," said Ibrahim al-Mugaiteb, head of the Saudi-based, independent First Human Rights Society.
"The problem is not the government, but the religious police," he said, referring to the morals squad that roams the streets implementing the dictates of the clergy.
Elsewhere in the Gulf, things are easier, but restrictions still apply. Christian leaders say governments struggle to strike a balance between the needs of their ever-growing foreign communities and the demands of their more conservative citizens.
In the United Arab Emirates, Christians may only worship in places with special licences. The authorities are slow to hand these out or to grant permission for new churches to be built.
Every Friday in Dubai, the UAE's business and tourism hub, crowds of worshippers swamp the few churches and licensed compounds.
"We have something like 16,000 cars trying to park around here on a Friday," says the Reverend Canon Stephen Wright of Christ Church Jebel Ali, an Anglican church in a compound on the outskirts of Dubai that accommodates six other denominations.
Next door to Christ Church is the Dubai Evangelical Church Centre, a complex of evangelical churches with big prayer halls, meeting rooms, library and an outside baptism pool.
""We'd love to have a lot of small churches across Dubai rather than one big one, but unfortunately in Dubai you can't do that," said Roy Verrips, the South African administrator of the United Christian Church of Dubai.
He says his church has about 500 members, but the complex draws around 3,000 Christians on Fridays for services in at least six languages from Tagalog to Korean, Nepali and Chinese.
"If this place wasn't here, we wouldn't be able to stay here. For me it's the most essential, most significant thing that we have as believers," said a Filipina Christian who works in Dubai as a housemaid and gave her name only as Gerry.
Verrips says his members do not try to convert Muslims, something forbidden in the UAE as in most Gulf Arab countries.
"We respect and work within the boundaries that they set for us," he said, adding that his church did nonetheless encourage its members to talk to people about Christianity.
Evangelical Christians who do proselytise end up creating difficulties for all the churches, as the angered authorities clamp down on everyone, several Christian leaders said.
Most are grateful for the limited freedom on offer. "There's no financial support, but otherwise I couldn't criticise the government for not being helpful," Qatar's Schwartz said.
"We're just thankful for what we have," said Verrips.
Additional reporting by Ulf Laessing in Riyadh, Raissa Kasolowsky and Tamara Walid in Dubai, Regan E. Doherty in Doha; writing by Raissa Kasolowsky; editing by Alistair Lyon