Change in Hospital Council Leadership: When James Barber takes over as president of the Hospital Council of Southern California today, he plans to steer the 71-year-old trade group into uncharted waters. Barber wants the nation’s largest metropolitan-area hospital association to bring doctors groups, health insurers and other providers into its fold--an ambitious plan for groups frequently at odds on legislative and other issues. But Barber, 39, says rapid consolidation in the Southland’s health care industry is blurring the lines between hospitals, medical groups and health plans, creating a convergence of interests. The consolidation is being fueled by the growth of managed-care companies, such as health maintenance organizations. Barber, the council’s executive vice president since 1989, succeeds Stephen W. Gamble, 65, who is retiring after 36 years with the council, the past 17 as president. During Gamble’s tenure, the council has grown from a three-employee group to one that employs 500 people and has branched out into several for-profit and nonprofit ventures. It represents 250 health care facilities in six Southland counties.