* Geagea votes eclipsed by blank ballots
* Rival Aoun says no clear consensus emerged
* Politicians say presidential poll could take months (Adds details, quotes)
By Laila Bassam and Dominic Evans
BEIRUT, April 23 (Reuters) - Lebanese parliamentarians failed to elect a new president on Wednesday in a first round of voting deadlocked by domestic rifts and the war in Syria, which has polarised Middle East states that traditionally broker Lebanon's political deals.
Leading candidate Samir Geagea, a former warlord who spent 11 years in prison after Lebanon's civil war, fell well short of the required two-thirds support in a vote that could be the first of many attempts to agree on a successor to President Michel Suleiman.
Geagea won 48 of the votes cast by 124 deputies. His total was eclipsed by 52 blank papers submitted by political opponents determined to block his campaign but who have yet to rally behind any rival candidate.
The stalemate was no surprise in a country whose sectarian divisions have been deepened by the three-year-old war in neighbouring Syria and which has frequently relied on regional powers to impose a settlement over bickering political factions.
That prospect is hampered by the devastating conflict in Syria where Saudi Arabia, which supports Lebanon's Sunni Muslim-led March 14 bloc, and Iran, which backs the Shi'ite militant Hezbollah and its March 8 allies, are arming opposing fighters.
"It's clear that no one has built a consensus around him," said former army chief Michel Aoun and prominent March 8 politician, who has made no secret of his own presidential ambitions but has yet to launch a campaign.
The 61-year-old Geagea was the only warlord to be imprisoned after Lebanon's 1975-1990 conflict, spending 11 years in jail for political murders and other killings, and was not expected to garner enough support for a successful challenge.
He was backed by the March 14 coalition which supports rebels fighting Syrian President Bashar al-Assad but opposed by March 8 parliamentarians led by Hezbollah, which is fighting in Syria for Assad against Sunni Muslim rebels and foreign jihadis.
In a clear protest against Geagea even standing for the presidency, a handful of ballot papers were filled out with the names of some of the people he was accused of killing during Lebanon's civil war.
Aoun led his own bloc of deputies out the chamber after the vote - preventing a second round in which the threshold for victory would be lowered from two-thirds to a half of deputies.
"We withdrew after the first round, while we await a consensus for a candidate," he told reporters.
The next round of voting will be held next Wednesday, parliamentary speaker Nabih Berri told deputies.
Lebanon's political system divides up political power among its various religious communities, allocating the presidency to Maronite Christians. The prime minister is a Sunni Muslim and the speaker of parliament a Shi'ite Muslim.
The search for a new president comes just one month after Prime Minister Tammam Salam, appointed in March last year, finally ended a year-long government vacuum when he won a vote of confidence in his new cabinet.
A prolonged delay in electing a president could put Lebanon back in limbo just when it most needs leadership to contain months of sectarian conflict and cope with a flood of Syrian refugees and a sharp slowdown in economic growth.
Suleiman, a former army chief like Aoun, was only picked as president in 2008 after six months of political argument, in a deal brokered by the Gulf state of Qatar.
Senior politicians have said the current presidential campaign could take just as long. A parliamentary election which had been scheduled for last summer was postponed until November 2014.
If parliament fails to elect a new president in next week's session, politicians might look for consensus candidates such as current army chief General Jean Kahwaji or Central Bank governor Riad Salameh, neither of whom has declared their intention to run at this stage. Other figures, low profile and potentially uncontroversial, may also emerge.
Geagea said he would continue his campaign. But with Druze leader Walid Jumblatt vowing to keep backing his own candidate, Henri Helou, who won 16 votes, there is little prospect of Geagea's fortunes improving and March 14 bloc has not committed to continue supporting him in any future round of votes. (Editing by Andrew Heavens)