The PEN American Center, the American branch of the international literary and human rights organization, has announced the appointment of Steven Isenberg, a lawyer and professor of literature, as its new executive director. Mr. Isenberg, who is also a former interim president of Adelphi University and publisher of Newsday, replaces Michael Roberts, who resigned in June. The philosopher, novelist and critic Kwame Anthony Appiah, president of the center’s board of trustees, said Mr. Isenberg combined “a love of literature and an unyielding commitment to free expression around the world” and “understands the critical importance of organizations dedicated to protecting” those values.