James de Castro, programming chief for AOL Time Warner Inc.'s America Online division, resigned after just seven months on the job.

His departure is yet another in a series of management changes at the online company. America Online, whose advertising revenue is plummeting and subscriber growth is slowing, is on its third chief executive in the past year and is finalizing a turnaround plan that it will present to AOL's board this month.

Mr. de Castro, 47 years old, said in an interview that he left because "I want to run a company." Colleagues said Mr. de Castro was disappointed that he wasn't chosen to head America Online. Instead, Jonathan F. Miller, a former lieutenant of media mogul Barry Diller, was hired as chief executive in August. One of Mr. Miller's first moves at the company was to take responsibility for the advertising sales division, which had previously reported to Mr. de Castro.

Mr. de Castro is a radio-industry veteran who rose from general manager of stations in Chicago to become vice chairman of AMFM Inc. during a period of rapid consolidation. He left after Clear Channel Communications Inc. agreed to acquire AMFM in 2000.

Robert Pittman, who was co-chief operating officer of AOL, hired Mr. de Castro to run the programming division in April. But Mr. Pittman abruptly quit AOL in July, after losing the succession race for the chief executive job. Since then, many of Mr. Pittman's former lieutenants have left the company.

During his tenure as president of the AOL Interactive Service, Mr. de Castro was praised for revitalizing the programming department that produces online news and features. He cut back on pop-up ads and beefed up the news that appeared on the America Online "Welcome Screen." He also brought some old media techniques to the online medium, dividing the programming into so-called day-parts so that certain features are shown at certain times of the day.

Now, Mr. de Castro's programming organization will report to America Online Vice Chairman Ted Leonsis, a veteran of the company. Mr. Leonsis, 46, said this will be his first operational role in about 18 months. Mr. Leonsis joined America Online in 1994 and was president of the company before Mr. Pittman's arrival in 1996. In 1999, Mr. Leonsis bought stakes in the National Hockey League's Washington Capitals and the National Basketball Association's Washington Wizards and began to focus more of his attention on those teams.