New York ? Women will anchor two of the three major network evening newscasts — still considered the premier jobs in the television news business — after ABC said Wednesday that Diane Sawyer will replace Charles Gibson, who is retiring at the end of the year.

Until Katie Couric became “CBS Evening News” anchor in September 2006, no woman had held the job done by broadcast legends like Walter Cronkite, Peter Jennings, Tom Brokaw, Chet Huntley, David Brinkley and Dan Rather alone. Barbara Walters, Connie Chung and Elizabeth Vargas have done it only when teamed with men.

Sawyer’s hiring is a “watershed moment,” said the Women’s Media Center.

“Diane Sawyer’s expertise and professionalism are without question,” said Carol Jenkins, president of the Women’s Media Center. “We look forward to her debut in January, and to the changes in the perceptions of women’s capabilities her reign will bring.”

Sawyer called the job “an enormous honor.” She’ll start in January.

“Diane is one of the hardest-working people I know and this new assignment is the latest achievement in an already accomplished and illustrious career,” said Couric, who competed against Sawyer as a host of NBC’s “Today” show. “And as I did, I’m sure that she’ll quickly find that she doesn’t miss that early morning alarm clock.”

Gibson, 66, who provided a steadying hand to a “World News” broadcast reeling from tragedy, said he had been planning to retire at the end of 2007 but events compelled him to stay. He was named anchor following the death of Peter Jennings and the wartime injury of Bob Woodruff in 2006. He’s been at ABC News for 35 years and says he plans to continue as an occasional contributor.

Gibson’s comforting presence made him an instant ratings hit at “World News” at a time the other networks had much younger anchors. But NBC’s Brian Williams eventually passed him by and has been leading in the ratings for the past year, with “World News” a solid second.

“The program is now operating at a very accelerated, but steady, cruising speed and I think it is an opportune time for a transition — both for the broadcast and for me,” Gibson said in an e-mail to fellow ABC News staffers. “Life is dynamic; it is not static.”

Sawyer was the obvious choice for a successor, said ABC New President David Westin. The 63-year-old newswoman has a lengthy resume that includes a stint on “60 Minutes” and competing with Barbara Walters for big news interviews in the 1990s. She’s done several documentaries in the past few years, including close looks at poverty in America.

Yet her departure leaves a hole at ABC’s “Good Morning America,” where she was the show’s centerpiece and co-host with Robin Roberts. ABC had no immediate announcement on what will happen on that show, though in-house candidates like Bill Weir and Chris Cuomo would be prospects to take a larger role. Morning news is dominated by NBC’s “Today” show, but a further slip from its second-place status would be costly for “GMA” and its parent Walt Disney Co.