TUNIS (Reuters) - Tunisia's prime minister-designate plans to retain the current defense, foreign and interior ministers but will name a World Bank official to take on the finance portfolio, sources close to coalition negotiations said on Friday.

Youssef Chahed, named premier after his predecessor was ousted in a no-confidence vote last month, has been in talks with the two main governing parties, the secularist Nidaa Tounes and Islamist Ennahda, over cabinet posts.

Chahed, a member of Nidaa Younes and ally of President Beji Caid Essebsi, has promised a cabinet capable of delivering economic reforms that have evaded past prime ministers, but opponents say he may not have the political capital to deliver.

Opponent say Chahed is inexperienced and too close to Essebsi, and he will need to overcome resistance from strong unions to austerity measures called for by Tunisia's multilateral lenders.

Tunisia's democratic transition since a 2011 uprising overthrew autocrat Zine El-Abidine Ben Ali has been praised as a model for the Arab world. But the North African country has struggled with Islamist militant attacks and slow progress on economic reforms needed to create growth and jobs.

Sources close to the negotiations said Chahed had decided to keep the incumbent interior, foreign and defense ministers but name Marouane El Abassi, a World Bank representative for Libya and economist educated in France, as his finance minister.

Chahed's new government must be presented to Essebsi, and then approved by parliament. Final negotiations were continuing with political parties.

"The new composition of the government will be announced soon and once we have approval, we will go straight to work," Chahed told reporters on Friday.

During his nearly two years in office, previous premier Habib Essid failed to overcome political infighting and deliver reforms including public spending cuts and improvements to laws to attract foreign investment.

(Reporting by Tarek Amara; Writing by Patrick Markey; Editing by Mark Heinrich)