* Christian leader Aoun will probably become next president

* Lebanon without president for more than two years

* Hezbollah MPs will attend voting session

* Aoun opponent Berri says his MPs won't boycott vote session

(Adds Nasrallah quote, context)

By Laila Bassam and Lisa Barrington

BEIRUT, Oct 23 (Reuters) - The leader of Lebanon's Hezbollah movement, Sayyed Hassan Nasrallah, said on Sunday the door to electing a president was "wide open" and his members of parliament would vote for ally Michel Aoun at a parliamentary session at the end of October.

Although Christian leader Aoun still faces opposition from some political figures and might not secure the two-thirds majority required to win a first round of voting, sources say he probably has enough support to win by a simple majority in a second round.

Lebanon has been without a president for more than two years, part of a political crisis that has resulted in a breakdown in many basic services and concerns about the country's stability.

Lebanon's former prime minister Saad al-Hariri said on Thursday he would back Christian leader Aoun to be president, in an arrangement which is expected to result in Hariri eventually being appointed prime minister again.

Sunni Muslim leader Hariri is a longtime opponent of Shiite Muslim group Hezbollah and his move to support Aoun encountered opposition from members of his own Future Movement party. Hariri stressed that his endorsement was a "political settlement" for the benefit of the whole country.

Nasrallah said: "The past few days saw an important development: a declaration by the Future Movement leader (Hariri) of his support for the nomination of General Michel Aoun for the presidency. The door is now realistically wide open for a successful presidential election."

Parliament will convene on Oct. 31 for a session to elect the president, the 46th such sitting since the term of the last president, Michel Suleiman, expired in 2014. Each of the previous sittings failed to gain the two-thirds quorum needed to hold a vote.

"At the next session to elect the president, all of (Hezbollah's parliamentary bloc) the Loyalty to the Resistance bloc will attend, God willing, and it will elect General Michel Aoun ... as president of the Lebanese republic," Nasrallah said

The position of president must be filled by a Maronite Christian.

The first round of voting requires two-thirds of Lebanon's 128 MPs to attend a session and a candidate will be elected president if they secure a two-thirds majority, or 86 votes.

If no candidate gets this number of votes, a second round of voting is held on the same day where a candidate requires a simple majority of 65 votes to win.

Aoun's most prominent opponent is Parliament Speaker Nabih Berri who also heads the Shiite Muslim Amal party which is an ally of Hezbollah.

Berri was quoted by the state news agency on Sunday as saying he would not "disrupt the quorum", implying his MPs would not boycott the parliamentary session.

Nasrallah spoke at a commemoration event for a Hezbollah military commander recently killed fighting in the Syrian city of Aleppo. Iran-backed Hezbollah is fighting alongside Syrian President Bashar al-Assad in the country's conflict.

(Reporting by Laila Bassam and Lisa Barrington; editing by Andrew Roche) ((lisa.barrington@thomsonreuters.com; +961)(0)(1954456;))