The mini-summit hosted by Lebanese President Michel Sleiman was hastily organised amid fears of Sunni-Shiite violence erupting in Lebanon following reports that the UN court probing Hariri´s 2005 murder was set to implicate members of the powerful Hezbollah.[break]
The Shiite Islamist party is backed by both Syria and Iran.
Abdullah and Assad are due to arrive together from Damascus at midday and will meet Sleiman before attending a luncheon to which members of Lebanon´s unity government -- which includes two Hezbollah ministers -- have been invited.
Syria was the main power broker in Lebanon when the Sunni Hariri and 22 others died in a massive bombing on February 14, 2005, and was subsequently forced to pull its troops from the country after a 29-year presence.
Damascus has consistently denied accusations that it had a hand in the killing.
Relations between the two countries have been on the mend since 2008, when diplomatic ties were established for the first time. Prime Minister Saad Hariri, son of the slain leader, has also made four trips to Syria in the past eight months.
Saudi Arabia, a staunch supporter of the slain Hariri, has played a key role in the rapprochement between the two countries.
Saudi and Syrian flags were on display throughout the Lebanese capital on Friday along with huge portraits of the king carrying a welcome message.
Security was also tight, with additional army and police deployed.
"The whole visit is about containing the situation for the immediate future," said Sahar Atrache, a Beirut-based analyst with the International Crisis Group think-tank.
"They are here to exert influence on their internal allies... to prevent a real escalation."
The Arabic-language daily An-Nahar, which is close to Hariri´s Saudi- and Western-backed coalition, called the summit "historic."
"This joint visit is historic and decisive because of its timing and the consequences it can have on a mounting crisis in Lebanon related to the tribunal," it said.
Fears of renewed conflict rose last week after Hezbollah leader Hassan Nasrallah said he knew that the UN tribunal probing Hariri´s murder was set to indict party members.
He made it clear that he would not accept such a scenario, accusing the tribunal of being politicised and part of an Israeli plot.
"The Arab leaders´ visit to Lebanon is an opportunity to show Arab unity in the face of this plot which aims to destabilise Lebanon and sow sedition," Hezbollah deputy Hassan Fadlallah told AFP.
"This would not be in the interest of the Lebanese or their Arab brothers."
Analysts say that in addition to threatening civil peace, an indictment of Hezbollah members would deal a blow to the party´s reputation and destabilise Hariri´s unity government.
The Saudi monarch is expected to press Assad to use his influence over Hezbollah to avoid a political stalemate or a sectarian conflict similar to the one that brought Lebanon close to civil war in 2008.
Friday´s summit is Assad´s first visit to Lebanon since 2002, and King Abdullah is the first Saudi monarch to visit the country since 1957.
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