Public Broadcasting Service President Pat Mitchell will leave the network when her contract runs out in 2006. Ms. Mitchell made the announcement today to employees in an e-mail message. She made a similar announcement during a meeting of PBS general managers over the weekend in Washington.

Though her contract expires next March, Ms. Mitchell has agreed to stay on until June 2006 to give the network time to find her successor.

“Many colleagues seemed surprised, and for that reason I want to make sure that you are aware of my decision,” she said in her e-mail, sent out at 4 p.m. (ET) Tuesday.

The message did not indicate why she had decided to leave. The network has been under ratings and financial pressure. Ms. Mitchell also has been criticized by both liberal and conservative organizations in recent days for her handling of a controversial episode of the children’s series “Postcards from Buster,” involving two lesbian parents. PBS initially said it would air the episode across its network, then withdrew that plan.

In her message to PBS employees, Ms. Mitchell listed her accomplishments: “the success of PBS Kids Go, our partnership with Comcast, HIT and Sesame Workshop for the new kids channel; the creation of a PBS Foundation; the launch of the Digital Funding Initiative (DFI); and our partnership with Google. All of these accomplishments are a result of your hard work!”

Insiders think a successor likely will come from within PBS’s ranks, and some station and network executives have indicated interest in the job.