By Asma Alsharif

MECCA, Saudi Arabia (Reuters) - Adalet Gigek sat impatiently in a crowded hotel lobby, waiting for the minibus to take her to Mecca's Grand Mosque for noon prayers as millions of Muslims started arriving in Saudi Arabia before the annual haj pilgrimage which starts on Friday.

She has spent five years hoping for the chance to fulfill her duty as a Muslim by performing haj and knows she will not be allowed to go again because pilgrim numbers are strictly controlled to prevent overcrowding.

"Each year for the past five years I checked with the authorities," said the 66-year-old mother of eight, a rosy pink scarf framing her beaming face. "When I finally found out I was selected I soared with happiness."

As one of Islam's five pillars, the haj is enjoined on all Muslims who are physically able to carry it out, but this year the pilgrimage follows uprisings across the Arab world and growing tensions between Sunni Muslim Saudi Arabia and Shi'ite power Iran.

Home to Islam's holiest sites, Saudi Arabia regards itself as the guardian of Islam and assumes the responsibility of maintaining a peaceful haj season when Muslims from various sects gather at the same place and time.

Although haj starts on the eighth day of the lunar month of Dhul Hijja, which falls this year on Friday, November 4, most pilgrims come earlier to visit the holy mosques in Mecca and nearby Medina, where the prophet Muhammad was buried over 1,400 years ago.

Over 1.5 million pilgrims have arrived in the Mecca region so far and Saudi authorities have spent freely to avoid any repeat of the deadly incidents which marred haj seasons in the past such as fires, hotel collapses, police clashes with protesters and stampedes.

TURBULENT YEAR

In a turbulent year for the Middle East, Saudi Arabia avoided the sort of protests which swept across the Arab world, toppling leaders in Tunisia, Egypt and Libya and leading to violent uprisings in Syria, Yemen and Bahrain.

King Abdullah instead offered support to allies who faced popular revolts and averted any similar protests inside Saudi Arabia with a ban on demonstrations and spending of $130 billion on housing and other social benefits.

"Allah did not intend haj to be a place for dispute, haggling... or using it for political agendas or preaching grim sectarianism," Saudi Arabia's Grand Mufti, Sheikh Abdulaziz Al al-Shaikh, said last week.

Riyadh fears Iran is behind an uprising by neighbouring Bahrain's majority Shi'ite population against a Sunni monarchy. It also said that a violent protest early this month by members of its own Shi'ite minority had been instigated by a "foreign power," widely interpreted as code for Iran.

Earlier this month, the United States said two Iranians had plotted to assassinate the Saudi ambassador to Washington with support from Tehran. Iran has denied the charges.

In 1987 clashes between Iranian pilgrims and Saudi security forces led to the deaths of hundreds of people.

During haj, Saudi religious police patrol the holy cities to ensure pilgrims are worshipping in the manner prescribed by the Gulf monarchy's strict interpretation of Islam.

"In terms of the government's security and services, all is good. The problem is only with the (religious police), they bother us while worshiping," said a turbaned Shi'ite cleric from Iraq.

"While I was praying one of (them) forced my hand open to confiscate a napkin because he thought I was hiding dirt in it to pray on it... as the Shi'ite tradition calls for," the man said, adding that some of his religious books were also confiscated.

In a separate incident, a Canadian Shi'ite cleric was arrested and later released in Medina after a skirmish with the religious police.

Saudi Arabia says it does not discriminate against Shi'ites.

PILGRIMAGE

To forestall any repeat of incidents such as the 2006 stampede in which hundreds of pilgrims died, the Saudi authorities have lavished vast sums to expand the main haj sites and improve Mecca's transportation system.

The Grand Mosque is the main attraction for over 6 million pilgrims who enter Mecca throughout the year, of which 2.5 million-3 million pilgrims are expected during the haj.

An expansion project will raise the mosque's capacity to allow it to hold 2 million pilgrims and install pedestrian bridges.

The area of Mecca around the Grand Mosque is also being transformed, as high-rise buildings are put up to cater for the large influx of visitors.

This month, the pilgrims will have full access to a $1.8 billion railway, which was launched at only 30 percent of its capacity last year, to ease pilgrim transport between holy sites around Mecca.

Among the rites they must perform during the three-day pilgrimage, hajis must walk seven times around the Kaaba, the cube-shaped building at the center of the Grand Mosque, pray at nearby Mount Arafat and ritually stone the devil by hurling pebbles at three walls.

Gigek, the Turkish pilgrim, is relishing an opportunity that has cost her more than 2,700 euros ($3,800) as well as her long wait.

"Many are still waiting for their chance," she said. "I know this will not happen again." ($1 = 0.705 euros)

(Reporting by Asma Alsharif; Editing by Angus McDowall and Roger Atwood)