BEIRUT, Oct 18 (Reuters) - Former Lebanese Prime Minister Saad al-Hariri intends to endorse Michel Aoun for the country's vacant presidency, political sources said, though a leading member of Hariri's party was quoted as saying the decision was not yet final.

The dramatic proposal would result in Aoun, a political ally of the Iranian-backed Shi'ite group Hezbollah, becoming head of state and the Saudi-backed Hariri becoming prime minister for the second time, the senior political sources said.

Political conflict has left the Lebanese presidency empty for 2 1/2 years. The post is reserved for a Maronite Christian in Lebanon's sectarian power-sharing arrangements.

It was not immediately clear if Aoun's candidacy would enjoy enough support among other Lebanese politicians to secure the necessary two-thirds quorum for the vote in the 128-seat parliament.

The next scheduled parliamentary session to elect a president is set for Oct. 31. Aoun's political opponents include the powerful politician Nabih Berri, who is parliament speaker and head of the Shi'ite Amal Movement.

Two senior politicians told Reuters that Hariri had expressed his intention to nominate Aoun, who is in his 80s, for the presidency as part of the power-sharing deal.

A third source, a member of Hariri's Future Movement, confirmed Hariri had expressed this intention, but members of his own parliamentary bloc opposed it.

Fouad Siniora, a former prime minister and head of the Future Movement's parliamentary bloc, told the newspaper Daily Star that Hariri had told his MPs on Tuesday that he had decided to support Aoun's candidacy for the presidency, but added that there was "no final decision yet on this matter".

(Reporting by Tom Perry and Laila Bassam, editing by Larry King) ((thomas.perry@thomsonreuters.com; Reuters Messaging: thomas.perry.reuters.com@reuters.net))

Keywords: LEBANON POLITICS/