UPDATE 1-ABC to tap Stephanopoulos as co-anchor of 'GMA'

NEW YORK, Dec 9 (Reuters) - ABC News plans to announce on Thursday that George Stephanopoulos will become an anchor of "Good Morning America" in a long-expected change that sees Diane Sawyer step up to head the U.S. network's nightly news.
Stephanopoulos, 48, is a former political adviser to the administration of President Bill Clinton. After leaving the White House, he took roles co-hosting ABC News coverage of political events and appeared regularly on ABC News shows.
He is expected to keep "This Week," his Sunday news program, "for the foreseeable future", one source said on Wednesday.
Stephanopoulos will begin his role on "Good Morning America" (GMA) on Dec. 14.
Robin Roberts will remain co-anchor at GMA, mow the second most-watched morning news program in the United States behind NBC's "Today."
Media reports have said Chris Cuomo, GMA's news reader, is leaving and will be replaced by JuJu Chang. The Washington Post reported Cuomo, son of former New York Governor Mario Cuomo, will move to co-anchoring the ABC news magazine "20/20."
News programs are among the more lucrative shows put on air by the networks. ABC is owned by The Walt Disney Co.
Sawyer will begin solo anchor duties at ABC's "World News" on Dec. 21, replacing Charles Gibson, who said he would step down in September.
Sawyer joins Katie Couric of the "CBS Evening News" as a female anchor of a major U.S. broadcaster's nightly news.
Couric, who left NBC's "Today" show to become the first solo female anchor of a U.S. nightly news program, has had a rocky tenure. Initially, her ratings jumped as viewers tuned in to see how she performed but viewership faded and, in recent years, has remained consistently below ABC and NBC.
Because of her viewership numbers, speculation has persisted that Couric plans to leave "CBS Evening News" before her contract expires in 2011.
Sawyer, who leaves GMA on Friday, may face similar scrutiny over "World News" viewership.
"That was a burden that Katie Couric had to bear," said Martin Kaplan, director of the Norman Lear Center and professor at the University of Southern California Annenberg School for Communications & Journalism.
"She was measured as a symbol of the new evening news ... someone who would have to make the transition from morning TV." (Reporting by Bernard Orr, Editing by Bob Tourtellotte and John O'Callaghan)