"Fox Morning News," the 2 1/2-hour morning show that debuts on Channel 5 on Monday, has signed David Bender, formerly of KNBC in Los Angeles, as weathercaster. That completes the major on-air team, along with anchors Lark McCarthy and Tim White ...

With South African anti-apartheid leader Nelson Mandela arriving in New York today for a whirlwind U.S. tour, Channel 9 has dispatched anchor J.C. Hayward to cover the story up close through Friday. Andrea Roane will sit in for J.C. as anchor of the 5 p.m. news during her absence ...

And Channel 7 will have anchor Renee Poussaint at JFK this morning when Mandela and his wife, Winnie, arrive ...

Incidentally, CNN principal Washington anchor Bernard Shaw will conduct a one-on-one interview with Mandela here on Monday morning. The cable network will air the taped interview in its entirety on broadcasts at 10 a.m. and again at 3 p.m. that day ...

Steve Emerson, former national security correspondent for U.S. News & World Report and co-author of "The Fall of Pan Am Flight 103," has joined CNN's special assignment unit as a contributing consultant ...

Channel 32 reports that last Wednesday's broadcast of "Evening Exchange," on which D.C. Mayor Marion Barry chose to make his announcement that he would not seek a fourth term, gave the local public affairs show its highest ratings ever ...

During the hour, audiences climbed from a 3.4 rating and a 7 share during the first 15 minutes to a 3.9/8 and then a 4.1/9 by 7:45 before tapering off to a 3.9/8 in the last 15 minutes. The 3.8/8 overall average compares with a usual 1/2 for the broadcast, according to a station spokesman ...

Each local ratings point represents 17,278 TV homes ...

Also on the Network News Front:

"ABC World News Tonight With Peter Jennings" had no trouble winning the network race for the 23rd week in a row with a 9.2 rating and a 20 share, far ahead of "CBS Evening News With Dan Rather" at 7.8/18 and "NBC Nightly News With Tom Brokaw and an Unnamed (but Good) Piano Player" at 7.5/17 ...

NBC, by the way, says that contrary to sweeps ratings compiled earlier from the 4,000 Nielsen "peoplemeters" for May, which showed "Nightly News" in third place with an 8.1 rating, behind ABC at 9.5 and CBS at 8.5, a compilation of the 100,000 Nielsen diaries maintained by viewers in 200-plus TV markets for the month puts NBC second with a 10.0 rating, behind ABC at 10.9 and ahead of CBS at 9.5 ...

The discrepancy of 4 million TV homes on average during May between the two Nielsen systems points up once again a major complaint against the current Nielsen peoplemeter system.

NBC News likes the overall Nielsen Station Index (NSI) figures a lot better than the Nielsen Television Index (NTI) figures because they represent the third consecutive sweep this season giving NBC second place ...

Meanwhile, the Committee on National Television Audience Measurement, which includes the three big networks and some cable networks, is finishing a report that sets out industry-wide criteria for a revised ratings system ...

CONTAM, as the group is called, plans to invite ratings companies, including Nielsen, Arbitron, the British-owned AGB system (which CBS hired in 1987-88 but which proved to be a bust with advertisers) and any other that wants to try, to come up with an alternative to the present system. They'd like to get the system in place by the fall ...

At the CBS News bureau here, where several major jobs are currently open, general assignment correspondent Jim Stewart and Hill correspondent Linda Tiara will be filling in on the White House beat pending the appointment of a permanent replacement for Norman Robinson, who has returned to New Orleans as an anchor for the NBC affiliate there ...

CBS News has been close to signing Michel McQueen, who covers the White House for the Wall Street Journal bureau, but so far she's resisted their blandishments ...

Over at "Nightwatch," which Charlie Rose has departed to anchor a new afternoon syndicated talk show for Paramount this fall, the talk is that CBS News president David Burke wants two anchors to replace the hard-working Rose. Producer Deborah Johnson is due to meet with Burke in New York on the new appointments next week ...

One possibility is National Public Radio's Scott Simon, who has filled in for Rose in the past. The other is almost sure to be a woman. Neither is expected to be from inside CBS News ...

For the next couple of weeks Terrence Smith will fill in for Rose, with Eric Engberg waiting in the wings for a stint in July ...

Over at "Face the Nation," which executive producer Karen Sughrue leaves at the end of the summer to join her husband in Berlin, the word is that an ABC News producer is high on the list as a replacement on the CBS News public affairs program ...

PBS president Bruce Christensen told public broadcasters meeting in Dallas yesterday that the network is planning a feasibility study with the Discovery Channel, aimed at forming a new cable program service "dedicated to education" ...

PBS, WGBH in Boston and WNET in New York have been studying possible approaches to establishing some form of public TV presence on cable, Christensen said ...

"After considering a number of possibilities," he said, the Discovery Channel was chosen ...

"We believe the combination of public television's programming resources and the Discovery Channel's cable expertise and its financial resources offers the most promise for a satisfactory relationship among our stations and their local cable operators" ...

He added that "at this early stage, we have very few answers" ...

TV RATINGZZZZ

Following are the top 20 network prime-time shows last week, ranked according to the percentage of the nation's 92.1 milllion TV households that watched, as measured by the A.C. Nielsen Co. A share represents the percentage of actual sets-in-use tuned to a particular program when it aired.

RATINGS....................................SHARE...NETWORK

1...16.8....Roseanne........................29.........ABC

2...16.7....Cheers..........................31.........NBC

3...14.7....The Simpsons....................28.........FOX

4...14.5....Married ... With Children.....26.........FOX

5...14.2....The Cosby Show..................28.........NBC

6...14.0....Empty Nest......................29.........NBC

....14.0....A Different World...............26.........NBC

8...13.8....Coach...........................23.........ABC

9...13.6....The Golden Girls................30.........NBC

....13.6....Seinfeld........................24.........NBC

....13.6....Designing Women.................23.........CBS

12..13.5....America's Funniest Home Videos..29.........ABC

13..13.4....NBA Portland-Det. IV (Tues.)....25.........CBS

14..13.2....NBA Portland-Det. V (Thurs.)....25.........CBS

15..12.9....Midnight Caller.................23.........NBC

16..12.8....60 Minutes......................31.........CBS

....12.8....Unsolved Mysteries..............25.........NBC

18..12.7....In the Heat of the Night........22.........NBC

19..12.6....The Wonder Years................23.........ABC

20..12.5....Murphy Brown....................21.........CBS

NBC won the week but FOX, with two programs (both reruns at that) in the Top Five for the first time ever, won the attention ...

NBC averaged a 10.4/20, followed by CBS at 9.7/18, ABC at 9.3/18 and FOX, with only 126 affiliates, at 5.7/11 ...

NBC's "Seinfeld" was the only original in the Top 10 as that network won Tuesday, Wednesday, Thursday and Saturday nights, CBS took Sunday and Monday and ABC won on Friday ...

The NBA playoffs on CBS concluded with the worst ratings since 1984 ...

Among the few highlights remaining on a week full of reruns, ABC's "Flockens" tied for 34th, NBC's "Singer & Sons" tied for 46th, the naughty Friday night movie on NBC, "Elvira, Mistress of the Dark," tied for 50th with ABC's "PrimeTime Live" and CBS News's "48 Hours" program on "gay bashing" tied for 53rd ...

NBC's "We'll Take Manhattan" tied for 57th, while the premieres of two game shows on ABC, "Monopoly" and "Super Jeopardy!" were 62nd and tied for 63rd, respectively ...

ABC research pointed out, however, that "Super Jeopardy!," despite a 7.0/17 performance, still won the 8 p.m. Saturday contest, the first time ABC has won that timeslot since Sept. 20, 1986, when the network premiered "Life With Lucy" ...

CBS's "The Most Dangerous Game" also was 63rd ...