David Muir replacing Sawyer at 'World News,' says ABC

NEW YORK - ABC News is making a generational change at the top of its evening newscast, replacing Diane Sawyer with 40-year-old understudy David Muir in an attempt to take a run at longtime ratings leader Brian Williams at NBC's Nightly News.

ABC also announced Wednesday that George Stephanopoulos will add the role of chief anchor for live news events and election nights to his current jobs as Good Morning America cohost and host of the Sunday-morning This Week political show.

The exit of Sawyer, 68, was not unexpected.

She will remain at ABC News to concentrate on doing prime-time specials and landing newsmaking interviews, where theoretically she will have less internal competition with Barbara Walters, semiretired, and Katie Couric, now at Yahoo.

When Muir starts as World News top anchor Sept. 2, it makes that role a men's club at the broadcast networks again, as he joins Williams and Scott Pelley of the CBS Evening News.

In a plugged-in world, network evening newscasts are a vestige of another time. Yet the three broadcasts together averaged 21 million viewers last week, with the audience usually smaller in the summer.

ABC has been a steady No. 2 behind NBC for years, even predating Sawyer's taking over as anchor in 2009, but has made inroads in recent months among younger viewers.

 Muir has been groomed for the job. He steps in as anchor when Sawyer is away, as he did last week, and once anchored the weekend newscast. His "Made in America" reports give him a high profile on World News and travel around the country.