NBC's "1986" registered a 11.7 national Nielsen rating and a 22 percent audience share Tuesday night, its second-best ld,10 sk,2 sw,-1 outing in six tries since its June 10 debut (12.3/23) . . .

Linda Ellerbee officially signed with ABC News yesterday to be a cohost for ABC's "Our World," the new historical news show that will compete against NBC's "The Cosby Show" and "Family Ties" on Thursday nights this fall, starting Sept. 25 . . .

The three-year contract, which will pay her a reported $350,000 annually, calls for her to write and cohost the program and do a commentary for ABC News radio . . .

In addition, she will bring her "TGIF" feature from NBC's "Today" show to "Good Morning America" for ABC Entertainment . . .

She reports to work in mid-August, she said yesterday . . .

Plans for Ellerbee to join a late-night talk show schedule, being considered by ABC Entertainment, are on hold, probably through the end of the year so she can devote full time to the primetime project . . .

"I just asked them to delay all that until later," Ellerbee said . . .

Should the late-night project come about, Ellerbee's salary could jump to $500,000 annually . . .

The witty, sometimes irreverent anchor had worked almost 11 years for NBC News, most recently on the "Today" show. But this summer, when the network asked her to take a 40 percent cut from her $250,000 salary during negotiations over a new contract, she left . . .

"It was an offer," she said yesterday, "I could refuse."

She subsequently was offered an anchor job on the about-to-be-changed "CBS Morning News," but the uncertainty of that project -- to say nothing of the early-morning wake-up calls -- prompted her to accept the ABC News offer instead . . .

ABC News President Roone Arledge said yesterday that her addition to "Our World" will "ensure its high quality" . . .

All in all, it's been a pretty good summer for Ellerbee. Her humorous book about her TV experiences, "And So It Goes," will be in fifth place this week on The New York Times best-seller list . . .

No cohost for "Our World" has been selected . . . although the names of Dick Schaap, Sander Vanocur and Jim Wooten have been bruited about . . . 'Profound Change'

Talks have broken down between the union representing network news broadcasters and ABC, CBS and NBC over the companies' demand that newspeople take on technical duties . . .

About 700 newspeople, working both at the networks and at their owned and operated stations, are represented by the American Federation of Television and Radio Artists (AFTRA) under two separate agreements . . .

The union and the networks have been holding talks since last October. The current contract expired Nov. 16. A week ago, the networks presented AFTRA with the far-reaching proposal regarding the technical duties . . .

According to AFTRA chief negotiator John C. Hall, the companies are demanding "the right to assign any newsperson not only to write and broadcast a story, but to operate the cameras, sound and other equipment, edit the story, feed it to broadcast stations and satellites and, in short, perform any and all technical and other functions in any way related to the assignment" . . .

He said such duties are now handled by five or more people . . .

Also affected would be members of the National Association of Broadcast Employes and Technicians (NABET) and the International Brotherhood of Electrical Workers (IBEW) -- the latter union covers radio technicians at CBS -- should the networks press the proposal . . .

CBS News Washington bureau correspondent Bob Schakne, chairman of the News Steering Committee for AFTRA, said yesterday that the proposal "involves much more than the technical issue. It affects the quality of journalism. It would be a profound change . . .

"If we're required to do those time-consuming chores it would seriously affect our basic job, which is to gather, write and report the news. It would be seriously damaging to our profession and we're very concerned" . . .

With the suspension of talks between the networks and AFTRA, union management is polling members for "their sense" of what steps to take, according to Schakne . . .

A meeting of correspondents from the Washington and Atlanta bureaus of all three networks was held here Tuesday. The network correspondents and newspeople from the New York O&Os met last night. Similar meetings are scheduled today and Friday in Chicago and Los Angeles, where other major network O&Os are located . . .

Other issues between the union and management include job security, severance pay and past management of the pension and welfare funds, according to both sides . . . Also in the News

Rozanne Weissman, director of public affairs for the Communications Workers of America, has been named vice president, corporate communications, for the Corporation for Public Broadcasting . . .

She replaces Ron Webber, who resigned in April . . .

Channel 32 has issued an invitation to be a part of live audiences for the taping of three programs tentatively titled "All-Star Comedy Showcase," which will air on WHMM sometime this fall . . .

The programs will feature local comedy talent, plus a comedian with a national reputation acting as cohost, according to a station spokesman . . .

The tapings, scheduled for 6 p.m. on July 28, Aug. 4 and Aug. 11, will be held at the Howard Inn, at Georgia Avenue and Bryant Street NW . . .

Because of limited capacity, the station asks those who would like to be in the audiences to call for reservations at 636-5600. That's 636-5600 . . .

The U.S. Information Agency says President Reagan's address on South Africa Tuesday was carried live, via five satellites, on the USIA's Worldnet network to at least 17 foreign cities . . .

That included Addis Ababa, Ethiopia. The Ethiopian minister of information told USIA that it was the first time in 10 years that Ethiopian TV agreed to carry a live broadcast from overseas, "including the Soviet Union" . . .

ABC News correspondent Lark McCarthy will be honored Aug. 1 by Alpha Phi Alpha, a nonprofit organization of professional men, when it presents its "Career Women's Program" in the Blackburn Center at Howard University, concurrent with the fraternity's 80th anniversary convention at the Washington Hilton hotel . . .

"CBS Evening News With Dan Rather" had a clear-cut first place in the network news race last week for the first time in a month . . .

For the week ending July 18, CBS averaged a 10.3 Nielsen rating and a 23 percent audience share, compared to 9.8/22 for "NBC Nightly News With Tom Brokaw" and 9.1/20 for "ABC World News Tonight With Peter Jennings." ABC blames ratings drop on preemptions on the West Coast the night of the network's coverage of the baseball all-star game last Tuesday . . .

The race among the reruns was tight, but NBC finished first last week with a 12.5 Nielsen rating and a 23 percent audience share (each rating point representing 859,000 TV homes) . . .

ABC was second with 12.2/23 and CBS was third at 12.0/23 . . .

CBS' "Silence of the Heart" was 25th, NBC's "Flight 90: Disaster on the Potomac" was 29th and part III of NBC's "Celebrity" tied for 32nd . . .

NBC's "She's With Me" was 34th, CBS' "The Thing" tied for 40th with "West 57th," part II of "Celebrity" was 44th and ABC's "Chameleon" was 46th . . .

Rounding out the Final -- And in Four Cases out of Five Fatal -- list for the week ending July 20 were, in order, ABC's "Benson," in 61st, followed by NBC's "Silver Spoons"; and ABC's "Diff'rent Strokes," "Ripley's Believe It or Not" and "The Colbys," all soap-operaed out at 65th and last place . . .