* Barclays CFO Lucas, General Counsel Harding to retire
* Will only leave when replacements found, likely to be some time
* Lucas under investigation for 2008 Qatar fundraising
* Lucas says appropriate time "to pass the mantle on"
By Steve Slater and Paul Sandle
LONDON, Feb 3 (Reuters) - Barclays said its finance director Chris Lucas and its top legal expert are to retire, adding to change at the top of the British bank as it struggles to put a series of scandals behind it.
Lucas, aged 52, has been finance director for a tough six years that spanned the global financial crisis, but the past nine months have been particularly difficult.
He is one of four current and former employees being investigated by UK authorities regarding a capital injection by Qatar in 2008.
Group General Counsel Mark Harding will also retire, the bank said in a statement on Sunday.
Both will remain in their roles until their successors have been found and an appropriate handover completed.
The bank said headhunters had been appointed, but it expected the process to take "a considerable time" to complete.
It could take up to a year to fill Lucas's position, people familiar with the matter told Reuters earlier on Sunday. Sky News first reported Lucas would leave.
Sources said Lucas's departure was not linked to the investigations into Qatar. He is also the only one of Barclays' executive directors still in his post after the bank was fined $450 million in June for rigging the Libor global benchmark interest rate.
New Chief Executive Antony Jenkins is attempting to move on from the bank's troubles, which also include the mis-selling of financial products, but that is proving a challenge.
The Financial Times reported on Friday that UK authorities are looking into allegations that Barclays lent Qatar Holding money to invest as part of the rescue fundraising four years ago.
British rules forbid a public company from giving financial assistance in order to acquire its shares.
Jenkins said Lucas and Harding both told him late last year they were considering stepping down. "Their decision to retire was theirs alone," he said.
Lucas has had health problems and although that has not affected his ability to do his job, it influenced his decision to retire, one of the sources said.
"Now is the appropriate time ... to begin my retirement from my role on the board and executive committee, and to pass the mantle on to a successor," Lucas said in a statement.
Jenkins is due to unveil plans to streamline and revive Barclays on Feb. 12 and he has also promised to improve culture and standards across the bank's 140,000 workforce.
The CEO said on Friday he will not take a bonus for 2012, saying he should "bear an appropriate degree of accountability" for the difficult year the bank endured.
"The execution of our change programme will take place over the next 5-10 years, and both Chris and Mark feel that now is the right time for them, personally and professionally, to pass the baton on in their respective roles to executives who can commit to seeing that programme to completion," Jenkins said.
Harding, 55, joined as general counsel in 2003, and has responsibility for legal issues throughout the bank, and as such handled Barclays' settlement with British and U.S. authorities last year for its manipulation of Libor rates.
Harding was previously general counsel of UBS's investment bank and a partner at law firm Clifford Chance.
Former Chief Executive Bob Diamond, Chairman Marcus Agius and Chief Operating Officer Jerry del Missier all left last year following the Libor scandal.
Lucas, who joined the Barclays board in April 2007 from PricewaterhouseCoopers, was paid almost 4 million pounds each year in 2011 and 2010, including long-term awards.
Jenkins and his chairman David Walker, are likely to be grilled on standards at the bank by British lawmakers when they appear before the UK banking inquiry on Tuesday.