Esther Wachtell, the president of the Music Center of Los Angeles County, will resign her $ 200,000-a-year post next July 15, but will stay on as a paid consultant and retain a position on the center’s governing board.“I just decided I could continue to serve the Music Center … in other ways, ” Wachtell said this week. She has headed fund raising for the downtown performing arts complex since 1988. A weak economy forced the Music Center to reduce fund-raising goals in recent years. It also cut support to four resident companies, including the L.A. Philharmonic and L.A. Music Center Opera. Wachtell said she wants to spend more time with her family.