Orange County’s top executive has been named the new Los Angeles County administrative officer by the Board of Supervisors. Thomas Mauk, a 35-year veteran of Southern California public policy and administration, will take over the position next month. He had been with Orange County since 2004 after serving positions in La Habra, Whittier and Norco. The nomination wraps a five-month search for the replacement to CAO David Janssen, who announced his retirement last summer and stepped down this month. The board had selected Sandra L. Vargas, county administrator for Hennepin County in Minnesota, for the job but she turned down the invite Jan. 16. In charge of the county’s 39 departments and nearly 100,000 employees, the CAO is widely considered one of the most influential positions in county politics and is sometimes called “the sixth supervisor.”