(Adds detail, background)

BEIRUT, Oct 20 (Reuters) - Lebanon's former prime minister Saad al-Hariri announced his support for his political foe, Hezbollah ally Michel Aoun, to become president in a televised news conference on Thursday, a step that may help resolve the country's political deadlock.

"This decision comes from the need to protect Lebanon and the state and the people ... but it is a decision that depends on agreement," he said, describing Aoun as "the only option left".

Lebanon has endured a protracted political crisis since parliament failed to elect a new president two years ago, paralysing government, causing a breakdown in many basic services and reviving fears of a slide back towards civil war.

The endorsement by Hariri, Lebanon's leading Sunni Muslim politician who has long opposed Aoun's Shi'ite ally Hezbollah, could break the prolonged standoff between Lebanon's political leaders.

However, Aoun will still face big obstacles towards his election as president by the country's parliament, including opposition from parliamentary speaker Nabih Berri, leader of the Shi'ite Amal movement which is also an ally of Hezbollah.

Hariri hopes to become prime minister again if Aoun becomes president. Hezbollah, Lebanon's most powerful political player, has not yet declared its position in detail, but had previously described Aoun - a Christian - as its preferred candidate

(Reporting By Lisa Barrington and Leila Bassam; Additional reporting by John Davison and Ellen Francis; Writing by Angus McDowall; Editing by Richard Balmforth; Editing by Kevin Liffey) ((angus.mcdowall@thomsonreuters.com; Reuters Messaging: angus.mcdowall.thomsonreuters.com@reuters.net))