(Adds Kouchner quotes in paragraphs 5-7)

By Laila Bassam

BEIRUT, Dec 7 (Reuters) - Lebanon's presidential election was postponed again on Friday, despite rival leaders' agreement in principle to give the post to army chief Michel Suleiman in a step that would ease the country's deep political crisis.

Lawmakers gathered at the tightly guarded parliament in downtown Beirut for a 1 p.m. (1100 GMT) session, only for it to be called off until noon (1000 GMT) on Tuesday, the seventh delay since the first attempt to hold the vote on Sept. 25.

Parliament Speaker Nabih Berri, a leading member of the opposition, announced the delay in a statement read on his behalf after holding talks with majority leader Saad al-Hariri.

The call for a new session on Dec. 11 showed the two sides believe they are within reach of a political deal that would ensure a two-thirds quorum for parliament to elect Suleiman.

French Foreign Minister Bernard Kouchner, who has been leading international mediation efforts, said he was "more than half optimistic" on the chances of a deal between the anti-Syrian ruling majority and the Hezbollah-led opposition.

Kouchner said there was "still a small chance for failure, but I have the feeling that the duty is accomplished".

Speaking to reporters before leaving Beirut, he said obstacles were being overcome but urged Christian opposition leader Michel Aoun, who has his own demands, to do more. "I think that general Aoun has to make an effort," he said.

One political source said: "Things are moving in the right direction, but more time is needed."

The presidency, reserved for a Maronite Christian under Lebanon's sectarian power-sharing system, has been empty since pro-Syrian President Emile Lahoud left office on Nov. 23.

RESPECT

Suleiman, 59, emerged as the consensus choice after Hariri and his allies dropped their insistence on electing a candidate clearly opposed to Syrian influence in Lebanon.

The army commander, who is on good terms with Hezbollah, was appointed to his post in 1998 when Syria controlled Lebanon.

Nevertheless, he has gained respect across the political spectrum for keeping the army neutral and curbing outbreaks of civil strife. He also won prestige from a 15-week army battle with Islamist fighters in a Palestinian refugee camp this year.

If elected, Suleiman will have to tread carefully if he aims to be a more unifying president than Lahoud, also a former army chief, whose term was extended in 2004 at Syria's behest.

Electing a president would help defuse a political crisis involving Western-backed factions and Hezbollah, allied to Syria and Iran, that has paralysed Lebanon for more than a year.

Sunni Muslim politician Hariri and Berri, who heads the Shi'ite opposition faction Amal, have met in the past few days in the presence of Kouchner, who has been shuttling between rival leaders to try to break the deadlock.

French officials have also been in touch with Syria and Iran to try to calm Lebanese disputes over the presidency.

This week's talks in Beirut have focused on the mechanism for electing Suleiman, shaping a national unity government and plans for a new law ahead of a 2009 parliamentary election.

Political sources said one obstacle was a demand by Aoun, Hezbollah's main Christian ally, that the next prime minister be a neutral figure, although his opposition colleagues were ready to accept a candidate chosen by the ruling majority.

Aoun wants enough seats in the next cabinet to reflect the size of his parliamentary bloc, the biggest Christian faction.

The rival camps also remain at odds over exactly how to amend the constitution, which bans senior public servants from running for office, to allow Suleiman to be elected.

Berri wants the amendment to bypass Prime Minister Fouad Siniora, while Hariri insists any move should go through the government. The opposition says Siniora's cabinet lost its legitimacy when all its Shi'ite members resigned last year. (Additional reporting by Nadim Ladki, Tom Perry and Rami Majzoub; Writing by Alistair Lyon)

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