Updated

Continuing a remarkable period of upheaval at the top ranks of broadcast news, ABC appointed Charles Gibson on Tuesday to replace Elizabeth Vargas as anchor of its hard-luck "World News Tonight" evening newscast.

Gibson starts Monday, and will continue on "Good Morning America" until the end of June. Vargas, who is pregnant, will return to "20/20" when she comes back from maternity leave in the fall.

With "World News Tonight" slipping in the ratings, ABC News can now position Gibson, 63, as the experienced hand against NBC's Brian Williams, 47, and Katie Couric, 49, who takes over at the "CBS Evening News" this fall.

"He has a wealth of experience, as well as an established relationship with the audience," said David Westin, ABC News president. "They know him, they trust him, they respect him. That would be an important factor here, no matter who the competition was."

The move marks a reversal from last fall, when ABC News was thrown into turmoil by the death of Peter Jennings. In searching for a successor after decades of declining influence and viewership for the evening news, Westin said his vision for the job — frequent travel and separate newscasts for the Web and West Coast television — was too much for one person.

Westin tried to install Gibson as interim anchor until Vargas and Bob Woodruff could take over, but Gibson balked at a short-term role. So the job went directly to the dual anchors — who were in place less than a month before Woodruff was seriously hurt in an Iraq bombing.

"I had a choice of giving up on the idea of the two anchors because I had lost one of my team members or going back to a one-anchor format with Charlie and I concluded that Charlie was the one who should take us forward at this point," Westin said.

Now Westin is removing Gibson from "Good Morning America" when it has an opportunity to make a move on NBC's leading "Today" show, with Couric leaving next week.

While the evening newscast is a network's flagship, they have an older audience and limited advertiser appeal. The morning news shows are where the money is made; "Today" show is by far NBC's most profitable program, earning some $250 million a year.

Gibson's appointment should end a period of rapid turnover at the evening news. It started when Williams replaced Tom Brokaw at NBC in December 2004. Jennings became sick with cancer the next spring and died in August. At CBS, scandal-scarred Dan Rather was ousted and replaced temporarily by Bob Schieffer, who has seen ratings jump. He'll give way to Couric in the fall.

Westin was criticized in some circles for not moving faster to shore up "World News Tonight" after Woodruff's injury. Westin said the move was timed to keep Gibson on "Good Morning America" for the full TV season, which ends this week.

Scrapped, for now, are the separate West Coast broadcasts. Gibson will take over the "World News Tonight" afternoon Webcast. He will have the job for an indefinite period of time.

"Because of circumstances, one joyous — Elizabeth's pregnancy — and the other terrible — Bob's injury — it didn't work out," Gibson said. "You look into the bullpen and you find the guy who's sitting there and stick him right in."

Gibson, however, cautioned that "I'm not (star Yankees pitcher) Mariano Rivera."

Woodruff, who suffered serious head injuries, will need many more months of recovery time and his return will be gradual, Westin said. "He'll always have a role on this program as an anchor — if and when he's ready for it," Westin said.

Woodruff, in a statement, called Gibson a mentor and friend: "I look forward to contributing to his broadcast as soon as I'm able."

Two weeks ago, "World News Tonight" slipped to third place behind Bob Schieffer at the "CBS Evening News" for the first time since 2001, although ABC recovered to beat the "CBS Evening News" by more than half a million viewers last week.

During the time they filled in for Jennings before his death last year, Gibson generally did better in the ratings than Vargas. But Westin said Tuesday's move "was not a ratings issue at all."

Vargas and singer Marc Cohn are due to have their second child in August. At age 44, Vargas said, it's been a difficult pregnancy and her doctors have asked her to reduce her schedule. She concluded that what will work best for her in the fall is to return to "20/20," the newsmagazine she co-anchors with John Stossel.

She said she didn't feel any pressure to step down.

"I won't lie to you, this was a difficult decision to make and I make it with a great deal of regret because I really enjoyed my time here," she said. Vargas said she hopes to anchor again, but doing a job that required frequent travel to dangerous places wouldn't be fair to a newborn and her other son, now 3.

Andrew Tyndall, a consultant who studies evening news content, said that by effectively demoting Vargas when she returns from maternity leave, ABC sends the wrong message to young women. With Vargas, "World News Tonight" has been devoting considerably more time to sex and family issues than its competitors, he said.

"The demotion of Vargas and her replacement by a pre-Baby Boomer not only makes ABC News' long-term strategy incoherent, it displays a woeful tin ear towards the very demographic ABC News was purportedly courting," he said. "What is the worst workplace nightmare the pregnant employee faces? It is the fear that her employer will find some way not to guarantee her job back on return from maternity leave."

Vargas said she made a decision about what's best for her family.

"Every woman has the right to make that decision for herself and her family without anybody judging it," she said. "My decision might not be the right decision for everyone else. My decision does not mean I'm stepping off the stage forever."

ABC, a division of Walt Disney Co., would not disclose terms of Gibson's deal. He was reportedly making in the range of $8 million to $9 million at "Good Morning America."

Asked whether he considered Diane Sawyer of "Good Morning America" for the evening role, Westin said he considered every conceivable possibility. "Diane, throughout this process, has said she thinks Charlie was the right person for this," he said.

Sawyer did not immediately return a call for comment. Gibson said he got her blessing for the move.

The network promoted Robin Roberts to one of three co-anchor slots at "Good Morning America" last year in anticipation that either Gibson or Sawyer would be needed elsewhere. It will continue with the Roberts-Sawyer team.

Gibson has been with ABC News since 1975, and worked as a reporter on Capitol Hill during the 1980s. He took over at "GMA" in 1987 and stayed until 1998. When ratings sank after his departure, Gibson returned and teamed with Sawyer a year later.

"There is certainly much reason to think that Charlie Gibson will be regarded in a league with Tom Brokaw," said Bob Zelnick, a former ABC News reporter now chairman of the journalism department at Boston University. "Both have a down-to-earth, plain way of addressing the audience, but they are extremely smart, careful and professional."