* "Extraordinary" measures because of "deteriorated" loanbook
* Provisional administrators named to overhaul BESA
* Follows Portugal's 4.9 bln euro rescue for parent BES
* Recent surge in Angola bad loans due to economy slowdown (Adds quotes, details on BESA's loans, deposits)
JOHANNESBURG, Aug 4 (Reuters) - Angola appointed administrators to manage the indebted local unit of Portugal's troubled lender Banco Espirito Santo on Monday and said a sovereign guarantee for most of its loans would be revoked.
Announcing "extraordinary overhaul measures", the central bank of Africa's second biggest oil producer, stopped short of nationalising Banco Espirito Santo Angola (BESA), one of the country's biggest lenders.
Citing the "deterioration" of BESA's credit portfolio, which it said had affected the bank's liquidity and solvency, the central bank said the new administrators would work with the bank's existing board, which would maintain day-to-day operations.
The measures closely followed Portugal's announcement of a 4.9 billion euros ($6.58 billion) rescue plan for BESA's Portuguese parent.
Banco Espirito Santo is to be split into a "good bank", renamed Novo Banco, and a "bad bank", which will house BES's exposures to the troubled Espirito Santo business empire as well as its Angolan subsidiary.
In its statement Banco Nacional de Angola, which did not name the provisional administrators appointed to run BESA, said a sovereign guarantee extended by Angola in December, of up to $5.7 billion, to cover most of BESA's loan book, would be revoked "in the initial phase of implementation".
"The overhaul measures aim to restore the financial and operational sustainability of the bank, bringing them into line with existing norms for banking activity in the country, but without contemplating, for the moment, the State's intervention in the social capital of the bank or the involvement of public funds," the central bank said.
"The existing board remains in office," it added, saying they would work with the administrators.
BESA's assets would be assessed and could be sold off or restructured, the Angolan central bank said, adding that deposits at the bank would be guaranteed, and its business relations with existing clients would remain unchanged.
The crisis affecting BES, Portugal's largest listed bank, had highlighted its exposure in the former colony of Angola, where BESA is a major financial player, with links to the ruling elite.
SURGE IN BAD LOANS
Many banks in Angola have been hit by a surge in bad loans in recent years due to an economic slowdown. The IMF sees Angola's real GDP growth slowing this year to 3.9 percent from 4.1 percent in 2013 and 5.2 percent in 2012.
BESA's total loans rose to 672 billion kwanzas ($6.9 billion) in 2012 from 350 billion two years earlier, according to a survey published last year by international accountancy firm KPMG, while deposits grew over the same period at a much slower pace, from 266 billion kwanzas to 349 billion, valuing its loan book at nearly twice its total deposits.
Angola broke its silence on the BES affair last month, when the central bank's governor Jose de Lima Massano admitted to parliament there were problems with BESA's credit portfolio that included bad loans and said BESA would need more capital.
In its statement on Monday, the central bank said it was announcing the overhaul measures for BESA because it had not to date received "unequivocal answers from the BESA shareholders about the possibility or terms of a capital increase".
The Angolan statement made no reference to the rescue plan for BES announced by Portugal late on Sunday, but Portuguese and Angolan officials have been discussing the crisis at the bank. ($1=97.8 Angolan kwanzas) (Additional reporting by Xola Potelwa and Ed Crople; Editing by Joe Brock and Greg Mahlich)