* SFO brings charges against Barclays' main operating arm
* Relates to support from Qatar during financial crisis
* Barclays says to fight charges (Adds detail, share price)
LONDON, Feb 12 (Reuters) - Barclays' legal problems deepened on Monday when Britain's Serious Fraud Office charged its operating subsidiary with providing unlawful financial assistance to Qatari investors during the banking crisis a decade ago.
The same charge was made against the bank's holding company last June, but it is the operating unit that is licensed for banking operations, meaning any conviction could also prompt sanctions from regulators.
The regulators are already separately weighing up how to respond to attempts by Barclays Chief Executive Jes Staley to unmask a whistleblower's identity.
Barclays said that Barclays PLC and its operating arm Barclays Bank PLC intend to defend the respective charges brought against them.
"Barclays does not expect there to be an impact on its ability to serve its customers and clients as a consequence of the charge having been brought," the bank said in a statement.
A loan to Qatar in November 2008 could have broken the law if the SFO can show it was connected with the Qatari payments to Barclays. Public companies are normally prohibited in the UK from lending money for the purchase of their own shares, a process known as financial assistance.
The Qatari investment helped to prevent Barclays from having to turn to the British government for a bailout during the financial crisis.
"The charges relate to financial assistance Barclays Bank Plc gave to Qatar Holding LLC between 1 October and 30 November 2008, which was in the form of a $3 billion loan for the purpose of directly or indirectly acquiring shares in Barclays Plc," the SFO said in a statement.
"This follows charges brought against the holding company, Barclays Plc, and four individuals in June 2017."
The SFO, which opened its investigation into Barclays in 2012, said a date for the first court appearance will be set in due course.
Barclays shares shrugged off the news, rising 1 percent to 194.9 pence by 0930 GMT, helped by a broader market rebound from last week's losses, and UBS raising its price target for the stock to 225 pence from 220 pence.
Two former top executives also face a charge of unlawful financial assistance.
The trial of Barclays PLC and four former top executives on a separate charge of conspiracy to commit fraud by false representation when they negotiated a capital injection for the bank from Qatar, is due to start next January. That separate charge has not been made against the operating arm
Qatar, which is a major UK investor, has not been accused of wrongdoing.
Analysts at Keefe, Bruyette & Woods said that while it was unhelpful for Barclays that the SFO has added charges, it should not change the dynamics of the case materially.
"However, it is negative that the group hasn't been able to settle a number of outstanding litigation issues, with outstanding litigation representing an unhelpful distraction to the management of the core franchise," the financial services firm said in a note to clients. (Additional reporting by Lawrence White; Editing by Kirsten Donovan and Keith Weir)