Arab leaders are stepping up pressure on Syria to resolve the Lebanese presidential stand-off by threatening to stay away from the Arab League summit in Damascus next month, a move that would deepen Syria's regional isolation.

Arab officials say the -Syrian regime's failure to influence its Lebanese allies is the main obstacle to the election of a Lebanese president, and that the summit at the end of March will fail unless Damascus pushes for compromise.

In a flurry of diplomacy, Egypt, Saudi Arabia and -Jordan have been trying to co-ordinate policy, hinting at either a boycott or a lowering of representation at a meeting that Damascus hoped would signal the end of its isolation. "All indications are that the summit is pending on the issue of Lebanon," said one Arab official. "If there's no agreement in Lebanon the summit has lost its importance."

Lebanon's presidency has been vacant since November and its parliament paralysed by a dispute between Lebanon's pro--Syrian opposition, led by the Hizbollah group, and the pro-western parliamentary majority.

In a power struggle that reflects the broader stand-off in the region between -pro-western Arab states on one hand and Syria and Iran on the other, the opposition has insisted on a consensus president and on winning a blocking minority in a new government.

Several rounds of mediation by the Arab League have failed to break the stalemate. Amr Moussa, the League's secretary general who is planning a trip to Damascus in the coming days, told Lebanon's al-Safir newspaper this week that the crisis was becoming more complicated and foreign influence had reached unprecedented levels.

Egypt and Saudi Arabia in particular appear convinced that Syria, which was forced to end its control over Lebanon in 2005, holds the key to a resolution of the crisis.

"The summit will be held in Syria and Syria has a role in Lebanon's problem, that's why I hope that Syria would solve the problem," Hosni Mubarak, the Egyptian president said recently. Syrian officials say they are doing all they can to help Lebanon but that it was up to political factions in Beirut to reach a compromise.

"The Syrian argument is 'We are trying' but they ask 'Why are you focusing on the fact that it is only us who has to put pressure on our allies? Why aren't other parties who have influence . . . in Lebanon being asked to do the same?' " said a League official.

Lebanese and other Arab officials doubt Syria will be swayed by the pressure from its neighbours. The League official said a successful summit could help Syria improve its relations with the Arab world but Damascus was not desperate to do that on any terms.

Since being ousted from Lebanon following the killing of Rafiq Hariri, former Lebanese prime minister and opponent of Syria, Syria's relations with other regional states have deteriorated.