* Co proposes to put some network assets into separate firm
* Assets valued at 13-15 billion euros
* Gives no financial details, timeframe
* Project needs approval of local regulator AGCOM
* Shares down over 5 pct after rising 14 pct in recent weeks (Recasts, adds source comments on regulator, analyst comments)
By Danilo Masoni
MILAN, May 31 (Reuters) - Shares in Telecom Italia SpA fell almost 6 percent on Friday, on disappointment ata lack of detail and no timeframe in a spinoff plan put forwardby the company late the previous session.
Telecom Italia agreed on Thursday to put some of its networkassets - valued at between 13 billion euros ($17 billion) and 15billion - into a separate company, with a view to selling astake in that new entity to state-backed fund Cassa Depositi ePrestiti (CDP).
But it offered little detail on the project, which requires regulatory changes and must be discussed with localwatchdog AGCOM.
A source familiar with the matter said Telecom Italia had informed AGCOM about its plan, but more information was neededbefore the regulator could take a decision, a process that couldtake a couple of months.
"We expect all the operators to be involved in this processand therefore full visibility on the implications for TelecomItalia could take some time," analysts at Espirito Santo said.
Ownership of the network implies Telecom Italia must abideby stricter rules than its rivals Vodafone, Fastweb and Vimpelcom's Wind. The Italian group wantsthese restrictions to be removed before the spin off, peoplefamiliar with the issue have said.
Shares in Telecom Italia were down 5.7 percent at 0.60 eurosby 1431 GMT, backtracking after rising 14 percent in the pastthree months.
One source with direct knowledge of the matter said thespinoff could take up to 18 months to complete, although a dealwith CDP could take less. CDP chairman Franco Bassanini onFriday said the spinoff ought to be carried out rapidly.
The idea of putting Telecom Italia's fixed-line copper andfibre network into a separate company follows political concernsover a proposed tie-up with Hutchison Whampoa.
Telecom Italia had said it would discuss a tie-up with theHong Kong-based conglomerate's Italian mobile phone unit, 3Italia, at a board meeting due to take place on June 5. ($1 = 0.7660 euros) (Editing by Lisa Jucca and David Holmes)