PETER Jennings yesterday was named sole anchor of "ABC World News Tonight," succeeding the late Frank Reynolds.

Reynolds died unexpectedly July 20, after suffering from viral hepatitis and cancer of the bone marrow.

Jennings had been called from his post in London six weeks ago to fill in for Reynolds as Washington anchor, on the expectation he would return to Great Britain on Reynolds' recovery.

With Jennings in the anchor seat, "World News Tonight" has recovered somewhat from the ratings loss suffered after Reynolds first left the air in April. That was undoubtedly a factor in choosing Jennings for the permanent role.

Jennings' new four-year contract reportedly will start him at about $900,000 annually.

While the appointment is effective immediately, Jennings will not make his first broadcast from New York, the new base for "World News Tonight," until Sept. 5.

Jennings also was named senior editor, a new title at ABC News designed to underscore his role in working with executive producer Bob Frye in determining the nightly content of the news show.

Dan Rather, anchor of "CBS Evening News," demanded, and received, the title of managing editor held by Walter Cronkite on that program when he replaced Cronkite in 1981.

Tom Brokaw, who likewise becomes sole anchor of "NBC Nightly News" Sept. 5, is also expected to add a similar title sometime this fall.

The appointment of the 45-year-old Jennings as solo anchor and the relocation of the ABC anchor position to New York, establishes several landmarks in the 20-year history of the 30-minute network news.

In replacing the 59-year-old Reynolds, Jennings joins Rather, 51, and Brokaw, 43, as a "new generation" of solo news anchors on the major newscasts. The move to New York reestablishes that city as the headquarters of the nightly news for all three networks.

Two weeks ago, NBC News announced that Roger Mudd, 55, would no longer coanchor with Brokaw from Washington, ending an on-again, off-again twin-city format for that network tracing back to the glory days of the Huntley-Brinkley Report, which ruled the ratings roost in the 1960s.

In 1978, ABC News president Roone Arledge instituted a triple-anchor concept, featuring Reynolds here, Max Robinson in Chicago and Jennings in London.

That concept, in recent years, has been more honored in the breach,however, as Reynolds was assigned the position of first among equals during his last year on the nightly newscast.

The choice of Jennings to succeed Reynolds has been almost certain since the latter's sudden death.

Arledge had become concerned about the "general disruption" that had affected the nightly news program as various correspondents and anchors from other programs took turns replacing Reynolds earlier this summer.

He felt that Reynolds had begun to establish "World News Tonight" as a serious contender and that the lack of a single, familiar anchor was largely responsible for the ratings drop that followed Reynolds' departure.

Arledge had predicted that upon Reynolds' return this fall, "World News Tonight" would leave "NBC Nightly News" behind in the two programs' five-year battle for second place and mount a serious challenge to number one "CBS Evening News."

In the shock following Reynolds' death, it quickly became apparent that ABC would seek his replacement within the network, if for no other reason than to halt any further "disruption" that might be caused by bringing in an outsider.

Jennings has been Foreign Desk Anchor and Chief Foreign Correspondent out of London since "World News Tonight" was recast in July 1978.

ABC sources yesterday said the Jennings move to New York will not affect the 20-person "World News Tonight" operation here, although two current senior producers on the show will be switched between the two cities and a writer will accompany Jennings to New York.

Exactly how the change will affect the bureaus in Chicago and London is not immediately known, though it is expected the Arledge will spend a considerable amount of money to recast the New York operation.

ABC hopes to have a new set ready for the Sept. 5 debut but more importantly in the long run, vis-a-vis the three-network news race, executive producer Frye and Jennings plan to revise the show.

"In the next few weeks," Frye said yesterday," we'll shake out a lot of things so that Peter's style, or approach, will become very evident in the broadcast, with a hard news orientation at the top, the breaking news story first and foremost.

"The whole reason for coming to New York changes the focus and dimension of the broadcast dramatically. It's the only way we can effectively work together."

In the past two years, CBS News, in particular, has deemphasized the nightly presence of Washington news on its telecast, usually by telling Washington-generated stories from locations around the country where the impact of a decision made here is likely to be felt.

And, when Mudd was demoted from coanchor two weeks ago, he suggested that Washington's role in the NBC News operation would be diminished, too, as a result.

Frye said yesterday, however, that "we will be retaining a very high Washington profile on the broadcast. Both Peter and I have had long experience in Washington and know how important it is in the news."

Jennings underscored that point yesterday, saying he'll "continue to spend a lot of time in Washington" where, he said, "we have our finest correspondents."

As for changes in the nightly show, Jennings said that "to be honest we don't know the answer to that. The most important thing for me is we have to figure out who we are broadcasting to. I'm not sure I have a terrific handle on that yet. The country's changing. Washington is going through different processes. We're racing into a political year. Bob and I will talk in the next couple of weeks."

NBC's Brokaw said yesterday that "the appointment of Peter is not unexpected. I've known Peter for a long timne. I wish him well. Not too well, but I wish him well. Beyond that, I probably shouldn't say anything."

CBS' Rather said "when a good man gets a good job, that's good news. I've known Peter since 1965."

As to what the change to solo anchor and the move to New York might mean for the future of the three-network race, Rather said, "I don't know and I don't think anybody knows. People are going to write about four anchors and a rudder but it's still coverage and content that counts."

In the most recent Nielsen ratings, issued yesterday, "CBS Evening News" continued to hold a comfortable lead with a weekly 11.1 Nielsen rating and a 25 percent audience share, compared with "NBC Nightly News' " 8.7/20 and "ABC World News Tonight's" 8.6/20 . . .

With the decision ratified that ABC was going to a solo anchor format, executives were quick to point out yesterday that negotiations with Chicago-based anchor Robinson on a new contract and a new assignment were continuing.

David Burke, vice president of ABC News, said, "We feel that for the last five years Max was a very important person in building 'World News Tonight.' And we've told Max that. Our talks so far have been very fruitful."

There have been reports that Robinson will be assigned as a national correspondent when his current contract expires at the end of this month.

The Canadian-born Jennings began his career in broadcasting in 1959 at CFJR, a radio station in Ontario. After work with the Canadian Broadcasting Corporation he became coanchor of that country's first network news show on a commercial network, CTV.

He joined ABC in 1964 and anchored the ABC evening news show "Peter Jennings and the News" from 1965 to 1967. After two years as a national correspondent, he served overseas in Rome and Beirut, until 1975. In 1976 he was Washington anchor and correspondent for "AM America" and became chief foreign correspondent the next year, joining the revamped "World News Tonight" in July 1978.

During his years with ABC News, Jennings has won several Overseas Press Club Awards as well as a George Foster Peabody Award.

He is married to Kati Marton, a former Bonn bureau chief and correspondent for ABC News and author of "Wallenberg." They have two children, Elizabeth and Christopher . . . TV Ratingzzz

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