By Angus McDowall
RIYADH (Reuters) - Saudi Arabia's King Abdullah appointed his son as governor of Riyadh Province on Wednesday in a move that strengthens his branch of the ruling dynasty as it approaches a difficult decision over how to transfer power to the next generation.
Prince Turki bin Abdullah's elevation to one of the most important positions held by ruling family members in the absolute monarchy comes months after another son of the king, Prince Mishaal bin Abdullah, was made governor of Mecca Province.
Moves in the ruling family are closely watched at home and abroad for clues on who will rule the world's top oil exporter, a country which also a huge influence over Muslims through its guardianship of Islam's holiest sites.
The Saudi line of succession does not pass directly from father to son, as in European monarchies, but has moved along a line of brothers born to the country's founder King Abdulaziz who died in 1954.
As that line nears its end, the al-Saud dynasty is grappling with how to move the succession down to the next generation of the family.
King Abdullah, who is over 90, has made a series of changes and appointments over the past two years that have consolidated the position of his allies in the family.
The most recent was the appointment of Prince Muqrin, the youngest of King Abdulaziz's sons to survive into adulthood, as deputy crown prince, a newly created position that makes him next in line to rule after King Abdullah and Crown Prince Salman.
That move was seen as delaying the moment when the al-Saud will have to decide on a prince from the younger generation to take charge, and prompted speculation about a wider deal between different branches of the family.
NEW DEPUTY DEFENCE MINISTER
Prince Turki's promotion from his previous job as deputy governor was made in a series of royal decrees carried on state media, which also removed the deputy defense minister, Prince Salman bin Sultan, from his post.
Prince Salman bin Sultan, a younger brother of former intelligence chief Prince Bandar bin Sultan, and a key figure in organizing Saudi Arabia's support for Syrian rebels, had met visiting U.S. Defense Secretary Chuck Hagel on Tuesday evening.
The decrees said Prince Salman had left the defense ministry position at his own request, a wording used every time a senior prince departs a post. He was replaced by the outgoing Riyadh governor Prince Khaled bin Bandar.
Until 2011, the position of Riyadh governor had been held for five decades by Prince Salman bin Abdulaziz, who was made crown prince in 2012.
The province is home to the country's capital and is the heartland of the al-Saud's traditional support base. Prince Turki bin Abdullah was born in 1970.
Besides appointing sons as governors of Riyadh and Mecca provinces, two of the three most important in the country, Abdullah has also made one of his sons, Prince Abdulaziz bin Abdullah, deputy foreign minister.
However, his most senior son, and the one seen as most likely to one day become king, is Prince Miteb bin Abdullah, who is head of the Saudi Arabian National Guard.
His main rival as a likely candidate to rule from among the next generation of the family is Interior Minister Prince Mohammed bin Nayef, say many Saudis and foreign analysts who follow the succession process.
(Reporting By Angus McDowall; Editing by Andrew Heavens)