FRANKFURT (Reuters) - Deutsche Bank's posted a fourth-quarter pretax loss of 2.6 billion euros ($3.5 billion) hit by hefty litigation and restructuring charges as the bank downsizes to a leaner investment banking environment under new leadership.

Germany's largest lender said strong operating results at its business divisions were overshadowed by a 1.9 billion euro goodwill impairment to pay for a new divisional structure and to hive off assets into a non-core unit.

The bank, which is being investigated for alleged manipulation of benchmark interest rates, also announced 1 billion euros in litigation charges in the fourth quarter, reflecting "adverse court rulings and developments in regulatory investigations."

"We embarked upon the path of deliberate but sometimes uncomfortable change in order to deliver long term, sustainable success for the bank. Simultaneously, we set the bank on course for fundamental cultural change," Co-chief executives Juergen Fitschen and Anshu Jain said.

"This journey will take years, not months," they added.

The lender is combining asset and wealth management divisions and creating a non-core division to hive off 125 billion euros worth of assets.

The corporate banking and securities division - Deutsche's main investment banking arm and traditionally its strongest performer - posted a quarterly loss before taxes of 548 million euros.

Deutsche Bank's net loss for the quarter was 2.2 billion euros.

In mid-December, it said fourth-quarter earnings will take a "significant" hit from the restructuring, which is designed to achieve annual cost savings of 4.5 billion euros by 2015.

($1 = 0.7370 euros)

(Reporting By Edward Taylor; editing by Victoria Bryan)