* A brother of Saudi king objects to deputy PM nomination
* He says nomination may make interior minister crown prince
* Prince Talal urges king to clarify his appointment
RIYADH, March 28 (Reuters) - A brother of Saudi Arabia's King Abdullah has started a rare public debate over the succession by questioning the appointment of the kingdom's interior minister as second deputy prime minister -- a position that would normally place him second in line to the throne.
The statement, by Prince Talal bin Abdul-Aziz, came after the Saudi royal court announced on Friday the appointment of Prince Nayef bin Abdul-Aziz as second deputy prime minister, a promotion that means he will run the kingdom when the monarch and crown prince are away.
The role would normally go to First Deputy Prime Minister Crown Prince Sultan, but he is convalescing in the United States after surgery earlier this year.
Prince Talal said the monarch needs to make sure the appointment served purely an "administrative purpose".
"I call on the royal court to clarify what is meant by this nomination and that it does not mean that he (Prince Nayef) will become crown prince," Prince Talal said in a faxed statement sent to Reuters.
"The latest nomination of the second deputy prime minister will give the impression that he will automatically become crown prince," said Prince Talal, who is also the father of billionaire businessman Prince Alwaleed bin Talal.
The statement was authenticated by a personal assistant of Prince Talal, who like both King Abdullah and Prince Nayef is a son of the kingdom's founder, the late King Abdul-Aziz al-Saud.
A CONSERVATIVE FORCE
Prince Talal said the appointment of Nayef as crown prince should be decided by the Allegiance Council, made up of the most prominent members of the al-Saud family who would vote to appoint future crown princes.
The decision to set up the council in 2006 aimed at replacing an even more opaque previous policy consisting of naming "the eldest and most able" son of late King Abdul-Aziz to the post of Crown Prince.
Prince Nayef, believed to be 75, is perceived as one of the most conservative forces in the kingdom and an opponent of reforms that may reduce the clout of both the monarchy and the religious establishment in the kingdom, the world's leading oil exporter.
He told reporters earlier this week that he does not see a need either for women to be members of a quasi-parliament or elections to its membership.
Prince Talal, on the other hand, has long been one of the most vocal supporters of reforms among the ruling al-Saud family.
An Interior Ministry spokesman declined to comment on the statement saying that only the royal court was eligible to comment on such issues. The court's public relations officials could not immediately be reached for comment.
Western diplomats and analysts said Prince Nayef's appointment improve his chances of becoming the next crown prince.
"There is no other explanation to this appointment. Prince Talal's statement reflects this," said Khalid al-Dakhil, a political science lecturer at King Saud University.
A diplomat added: "It is fair to talk about the Allegiance Council if there is a vacancy. Prince Nayef's appointment suggests the inevitability that he is to become crown prince".
A Saudi analyst close to official circles said Prince Nayef's appointment followed discussions among the top members of the royal family, but could not say if Prince Talal took part in these talks.
"Everything is possible behind those closed doors, they have agreed. The law allows the king to name one deputy or several deputies or remove them ... The allegiance council is not needed now since the position of crown prince is not vacant".
The appointment of Prince Nayef, which a royal decree said was "made in the interest of the public good", will put the interior minister in charge of running Saudia Arabia during an expected two-week absence by King Abdullah.
The monarch is expected to attend an Arab summit next week in Qatar before heading to London for a G20 summit early in April.
Diplomats and analysts say Prince Talal's push for reforms is shared by only a minority of several thousands of Saudi princes. "He has a history," one diplomat said.
Saudi authorities revoked in the early 1960s Prince Talal's passport when he sought to press for a constitutional monarchy and allied himself to late Egyptian President Gamal Abdel Nasser, then an arch-foe of the Saudi monarchy.
Prince Talal later toned down his rhetoric to be able to return to the kingdom.
Over the more than 30 years he has spent as Interior Minister, Prince Nayef has had to deal with a bloody siege at the Grand Mosque of Mecca in 1979 and a wave of bombings led by al-Qaeda sympathisers and aimed at toppling the monarchy.
(Editing by Samia Nakhoul)