Lebanon's opposition agrees to join Hariri govt

* Opposition, including Hezbollah, agrees to join govt

* PM-designate Hariri set to announce new government in days

* Hezbollah likely to have two ministers

(Adds details of proposed government, more background)

By Laila Bassam

BEIRUT, Nov 6 (Reuters) - Lebanon's opposition, including Iranian-backed Hezbollah, agreed on Friday to join a national unity government proposed by Prime Minister-designate Saad al-Hariri, a senior opposition source said.

"The Lebanese opposition has approved the proposed unity government," the source told Reuters after opposition leaders held a late-night meeting.

The source said the opposition would officially inform Hariri of its decision on Saturday and expected the new government to be formed in the coming two days.

Hariri's spokesman was not immediately available to comment on the report.

Hariri, who is backed by the United States and Saudi Arabia, was nominated as prime minister-designate after he led his anti-Syrian coalition to victory in parliamentary election in June.

He has spent more than four months trying to broker a deal with the opposition to join a unity cabinet. A warming of ties between the two sides' main backers Syria and Saudi Arabia in recent weeks helped ease the rift in Beirut and led eventually to the breakthrough.

The rival factions had agreed in July on the broad division of seats in the new cabinet. But Hariri, son of assassinated statesman Rafik al-Hariri, had struggled to reach agreement with opposition politicians on the details.

At the heart of the dispute were the demands of Christian leader Michel Aoun, an ally of Hezbollah. Aoun's Free Patriotic Movement holds more seats in parliament than any other Christian party.

The new 30-minister cabinet is set to include 15 ministers from Hariri's coalition, 10 from the opposition including two Hezbollah ministers, and five, including the key interior and defence portfolios, will be nominated by President Michel Suleiman.

Incumbents Ziad Baroud and Michel al-Murr, loyal to the president, are set to keep their interior and defence portfolios, while new foreign and finance ministers are expected to be named.

Hariri had named Raya Hassan for finance minister, responsible for managing Lebanon's massive public debt burden, in an earlier proposal that was rejected by the opposition.

Parliament Speaker Nabih Berri, the main Shi'ite Muslim ally of Hezbollah, is set to name the new foreign minister, political sources said. (Writing by Nadim Ladki; Editing by Alison Williams)