BEIRUT, Feb 25 (Reuters) - Lebanon's Western-backed governing coalition and its Syrian- and Iranian-backed opposition have failed yet again to reach a deal to end the country's political conflict, an Arab mediator said on Monday.

In the absence of a deal, a presidential election set for Tuesday looked set for postponement. It would be the 15th delay of a parliamentary vote expected to confirm army chief General Michel Suleiman as president.

Arab League Secretary General Amr Moussa said more time was needed to reach a deal between the rival camps, whose conflict has paralysed much of government for 15 months and left the country without a president since November.

"I had hoped that we would end with a comprehensive paper, or a comprehensive draft deal," Moussa said.

"But it appears that the matter needs more time," he told reporters after chairing a meeting between governing coalition leaders Saad al-Hariri and Amin Gemayel, and Michel Aoun, who represented the opposition.

The rival camps have agreed on Suleiman as the next head of state but are still at odds over how to share seats in a new cabinet to take office once he is elected.

The crisis threatens to undermine an Arab summit scheduled for March 29-30 in Damascus, which is blamed by Hariri and his allies for the crisis.

King Abdullah of Saudi Arabia and other Arab leaders who support the governing coalition are unlikely to attend the summit unless the Lebanon conflict is resolved, diplomats and analysts say.

Moussa, a former Egyptian foreign minister, said he hoped Suleiman would be elected before the summit.

"It is not impossible," he said.

Parliament Speaker Nabih Berri was expected to announce the official postponement of the presidential election later. The vote cannot take place unless the rival camps reach a deal that would ensure a quorum of lawmakers in the chamber. (Writing by Tom Perry, editing by Nadim Ladki and Mary Gabriel)

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