* Panels to sketch out criteria for new CEO
* Cenbank wants explanation of chairman's exec role
* Bank won't be influenced by politics -UniCredit chairman
* Unions call Profumo exit "irresponsible"
* Shares up 1.15 percent, sector down 0.9 percent (Releads with committee meetings, adds union reaction)
By Gianluca Semeraro and Ian Simpson
MILAN, Sept 23 (Reuters) - Italy's biggest bank UniCredit SpA took a first step on Thursday in picking a replacement for its chief executive, who resigned this week in a power clash with shareholders.
The board's strategic, governance and remuneration committees began to prepare the criteria for a successor to Alessandro Profumo, but there is still no list of candidates, said a source close to the issue.
Profumo quit on Tuesday amid board rancour over Libyan stake-building and flagging results.
Vice Chairman Luigi Castelletti told reporters after the meeting: "Everything is calm."
The departure of Profumo, Europe's longest-serving bank chief executive, has left UniCredit rudderless as it struggles to recover from the financial crisis and a series of acquisitions. Chairman Dieter Rampl is acting chief executive and has vowed to replace Profumo in a matter of weeks.
The Bank of Italy underscored the need for a quick replacement for Profumo, who steered UniCredit in its rise from a regional lender to a pan-European player operating in 20 countries. The central bank's supervisory unit asked UniCredit in a letter to explain Rampl's executive role and clarify how long it will be before a replacement is found. Italian rules prohibit a chairman from taking an executive role, barring exceptional circumstances.
UniCredit must also explain Profumo's severance payment and how it was arrived at, the letter said. Newspapers have said he is receiving a 40 million euro ($53.6 million) payout.
LIBYAN SHAREHOLDING
Libya's shareholding -- and Profumo's possible role in it -- sparked fear among politically linked shareholder foundations that he was trying to marginalise them.
Libya's central bank and Tripoli's sovereign wealth fund have a combined stake of around 7.6 percent. Bank rules bar a single shareholder from having a voting stake of more than 5 percent.
Profumo's departure was seen as a significant victory for the foundations and for the federalist Northern League, which is a partner in Prime Minister Silvio Berlusconi's conservative government. The League controls two of the regions in which the foundations are based.
However, in an interview with Corriere della Sera newspaper, Rampl denied that politics had influenced the bank.
He also declined to comment on a successor. In a letter to staff on Wednesday, he said a replacement could come from outside the group.
MF newspaper reported Economy Minister Giulio Tremonti wanted Italian institutional shareholders to propose Treasury Director General Vittorio Grilli as CEO.
Claudio Costamagna, a former Goldman Sachs executive, told reporters he was not interested in becoming chief executive after some reports had named him as a possible candidate.
The board's decision to accept Profumo's resignation was criticised in a joint letter from eight UniCredit labour unions. They called the move "irresponsible", given a wide-ranging restructuring planned in Italy.
Shares in UniCredit were up 1.15 percent at 1.844 euros at 1435 GMT. The STOXX Europe 600 banking index was off 0.9 percent. (Editing by David Cowell) ($1=.7461 Euro)