The five-time, Emmy-winning actor-writer-director will play a Republican U.S. senator from California who plans to run for president.
The cast will also feature Marley Shelton as a former newspaper feature writer who joins the White House staff as assistant press secretary. The Reporter said Jimmy Smits -- formerly of "NYPD Blue" and "L.A. Law" -- was in talks to join the "West Wing" cast this season as well.
Alda -- who won Emmys for acting, writing and directing on "M*A*S*H" -- was nominated for an Emmy in 2000 for Outstanding Guest Actor in a Drama Series, for his performance as Dr. Gabriel Lawrence on "ER."
"The West Wing," which has won four Emmys for Outstanding Drama Series, is returning for a sixth season on NBC this fall.