ABC News has formally named longtime correspondent Martha Raddatz as co-anchor of its Sunday morning program “This Week with George Stephanopoulos.”

Raddatz, ABC’s chief global affairs correspondent, has alternated in the “This Week” anchor chair with Stephanopoulos and has been a regular contributor to the public affairs program.

“Over the past several years the show has risen to great new heights with George, our chief anchor, at the helm, and with Martha playing a key role in anchoring and reporting for the program from Washington and from around the globe,” ABC News president James Goldston wrote in a memo to staffers announcing Raddatz’ appointment.

The personnel maneuvers take place after Stephanopoulos has taken on many more duties at ABC News. He is a co-host on morning show “Good Morning America” and also the news unit’s chief anchor, tasked with taking the desk when stories of national or global importance break. Internally, Stephanopoulos’ favorite duty is said to be the Sunday public-affairs program.

The competition in this particular arena has grown more heady in recent months, with both NBC and CBS instilling new faces in front of the camera at “Meet the Press,” where Chuck Todd holds forth, and “Face the Nation,” where John Dickerson took over duties once in the hands of Bob Schieffer.

Raddatz joined ABC News in January, 1999 as the network’s State Department correspondent. She also served a time covering the White House before being named chief global affairs correspondent. Prior to joining ABC News, she worked for NPR and Boston’s WCVB.

With Raddatz’s promotion to co-anchor, ABC News has tabbed chief White House correspondent Jonathan Karl as substitute “The Week” anchor.