WASHINGTON —  Pat Mitchell (search), the Public Broadcasting Service (search) chief under fire for spending public money on a cartoon show that also featured a real-life lesbian couple, will step down when her contract expires in June 2006.

Mitchell, the nonprofit network's fifth president and chief executive officer, also faced significant fund-raising challenges.

She drew recent criticism from both liberals and conservatives for "Postcards From Buster," (search) in which the title character, an animated bunny named Buster, traveled to Vermont — a state known for recognizing same-sex civil unions. Though the focus was on farm life and maple sugaring, the episode, entitled "Sugartime," featured an actual lesbian couple.

Newly appointed Education Secretary Margaret Spellings (search) contended that the episode did not fulfill the intent Congress had in mind for programming and said many parents would not want children exposed to such lifestyles.

Mitchell, 62, who joined PBS in 2000, told PBS managers at its annual meeting Monday that she would not seek a third three-year term when her contract expired in June 2006. In a statement to the media, Mitchell made no reference to the "Buster" controversy.

The network decided not to distribute the episode to its 349 stations. But the Boston public television station, WGBH-TV, which produced the series, has made it available to other stations.

PBS depends on Congress to for funding and also relies on contributions from individuals, local stations, state governments and foundations. The network receives money for the "Postcards from Buster" series through the federal Ready-To-Learn program aimed at helping young children learn through television.

Under Mitchell's leadership, prime-time ratings rose to the highest ever and PBS stations extended their reach for digital broadcasting to over 89 percent of the country.

Mitchell also added diversity to the schedule — including the "American Family," an emmy-nominated series featuring a Latino family, and "American Mystery!" a special featuring Indians living in the Southwest.

At the meeting with managers, Mitchell outlined an agenda for the remainder of her term, including securing sustainable funding on a national and local level, broadening public television's reach and resources in education and setting new benchmarks for children's programming.

"We have a lot to do in the next 15 months," she said in the statement. "I have a big agenda and am happy to be in the midst of spearheading some of PBS' greatest successes."