* PM Ivanishvili says his work done after beating Saakashvili
* Garibashvili seen easily approved by parliament
* Prime minister post now most powerful in country
By Margarita Antidze
TBILISI, Nov 2 (Reuters) - Georgia's prime minister on Saturday proposed his close ally, Interior Minister Irakly Garibashvili, to succeed him when he steps down in the next few weeks.
Billionaire Bidzina Ivanishvili has said he will quit as premier after Georgy Margvelashvili is sworn in as president on Nov. 17. The prime minister's position is now the most powerful in the former Soviet republic under constitutional changes which transferred many of the president's responsibilities.
Garibashvili still has to be nominated by parliament and approved by Margvelashvili, but both steps are a formality as Ivanishvili's Georgian Dream coalition dominates the assembly and the president is an ally of Ivanishvili.
Margvelashvili was elected last month to take over from pro-Western Mikheil Saakashvili, who spent a decade in power.
The election cemented Georgian Dream's grip on power, putting it in charge of the presidency for the first time, as well as the government and parliament which it took control of in a parliamentary election in October last year.
Ivanishvili says the departure of his bitter rival, Saakashvili, means his job is now done, two years after entering politics following a business career in which he made a fortune estimated at $5.3 billion.
But he could continue to wield influence as he dominates politics in the South Caucasus country of 4.5 million, which fought a five-day war with Russia in 2008 and is crossed by pipelines that carry Caspian oil and gas to Europe.
The current government must resign after the inauguration. The parliament then has one week to agree on a nominee for post of prime minister, to be appointed by the president.
Ivanishvili, who will be acting premier during that week, will hand over his functions on Nov. 24 and a new cabinet will be proposed by his successor, to be approved by parliament.