NBC News was the winner by a narrow margin over ABC yesterday when Nielsen released national ratings for the four days of testimony last week by Lt. Col. Oliver North during the Iran-contra hearings ...

Averaging the morning and afternoon sessions for Tuesday through last Friday, televised on all three commercial networks, NBC averaged a 5.4 rating and a 19 percent audience share, compared to ABC's 5.3/18 and CBS' 5.0/17 ...

Each rating point represents 874,000 TV homes ...

Daily overnight ratings from 15 big cities throughout the week had given ABC the lead, followed by NBC and CBS ...

For all the talk in the media about the popularity of the hearings, CBS research said average audiences during the week of North's appearance were down 4 percent from the previous week's three-network average, from a combined rating of 16.3 to 15.7 (a drop of about 700,000 homes, overall) ...

Within the business, the inability of CBS to hang on to its usual daytime supremacy was the big story -- a complete reversal of regular daytime viewer preferences. In the most recent weekly ratings for regular daytime programming -- soap operas and game shows -- CBS had averaged a 6.0/22, ABC a 5.6/19 and NBC only a 4.8/18 ...

Even the presence of Dan Rather throughout the week in Washington didn't help CBS. But David Poltrack, vice president of research for CBS, pointed out yesterday that the daily lead-in for Rather & Co. for the 9 a.m. start of the hearings was the undernourished "The Morning Program," which averaged only a 1.9 rating and a 10 share last week for CBS (it was pre-empted on the West Coast) ...

"As a matter of fact," said Poltrack, "we got stronger every afternoon. Basically, we're very close together; the margin of difference between the three networks with these numbers is almost negligible" ...

By comparison, hearing coverage on NBC each morning picked up a "Today" audience that averaged a 4.5/24 and, as a News division program, emphasized hearing stories. NBC ran "Today" on the West Coast between 9 and 11 a.m., during the lunchbreak back in Washington. ABC's "Good Morning America," which was also pre-empted on the West Coast for four days, averaged a 3.6/21 ...

Regardless of those factors and the narrowness of the win, NBC News was pleased with its success...

"NBC News has a growing reputation," said News vice president Tim Russert. "In times of crisis, people are making a conscious choice to watch NBC. You compare those regular viewing figures with the hearing figures and you have to say CBS collapsed" ...

In other news about the Iran-contra committees, the National Captioning Institute has announced that starting with this morning's hearings, real-time captioning of testimony will begin daily on PBS and whenever ABC or NBC is scheduled to broadcast in the three-network rotation ...

CBS does not have the equipment necessary for the real-time closed captioning for the hearing-impaired. On those days -- such as today -- when CBS is due to broadcast the hearings, only PBS will carry the special service ...

Funding for the real-time captioning is being allocated from a three-year, $5.3 million grant by the U.S. Department of Education set aside for NCI captioning of news and public affairs programs ...

NCI estimates that about 600,000 hearing-impaired viewers are reached through the 150,000 decoders currently in use around the country. More than 20 million people are hearing-impaired to some degree in this country, according to NCI estimates ...

More on Hearings The Post-Newsweek Stations -- which include CBS affiliates in Jacksonville, Fla., and Hartford, Conn., an ABC affiliate in Miami and an NBC affiliate in Detroit -- are by-passing the three-network rotation system which went into effect yesterday and providing direct daily coverage of the hearings to all four stations from their Washington bureau ...

The coverage, anchored by Tina Gulland and Tom Walker, will use the daily pool feed from the Hill ...

Joel Chaseman, president of Post-Newsweek Stations, yesterday criticized the networks' decision to rotate hearing coverage ...

"We deplore their timing," said Chaseman. "It confirms our worst critics, who say we're always there when it's exciting but fall away when it isn't glamorous. If you cover Fawn Hall or Ollie North, you have an obligation to cover others who aren't as 'exciting' but are also important to the story" ...

And this note to viewers who have wondered why, if they have a couple of sets in the house or at work turned to different stations covering the hearings, the testimony is sometimes out of sync ...

It's because Channel 9 (CBS) and Channel 4 (NBC) broadcast signals that have already made two round trips via satellite to New York and then back to Washington. The 90,000-mile journey can delay signals up to half a second ...

Channel 7 gets its ABC signal from New York but it's traveled up there and back by land lines and is nearly instantaneous. And, although other PBS stations receive a signal via satellite, Channel 26 here is getting its signal direct from Capitol Hill via land line ...

Cable News Network also uses a satellite ...

Also in the News CBS announced yesterday that it will air "CBS Reports: The Battle for Afghanistan" on Wednesday, July 29, starting at 10 p.m. ...

Dan Rather will anchor the report, which will feature film reports from cameraman Mike Hoover, summarizing "key battles that have taken place over the past three years" during the Soviet invasion ...

Channel 5 said yesterday that the appearance of Eddie Murphy (finally) Monday night on Fox Broadcasting's "The Late Show" has boosted ratings for the former Joan Rivers vehicle to possible record highs for this market...

During the first three nights Arsenio Hall hosted the program this week, it averaged a 7.0/15 on Five, and that includes a 9.1/21 on Monday night when Murphy, who reneged on a promised showing the previous week, finally appeared (each rating point represents 15,800 local TV homes) ...

Channel 5 also announced that "The Late Show" will be broadcast "live" again starting Monday, Aug. 3 ...

Oh. And the two-hour premiere of "Werewolf" on the Fox network last Saturday night had a national Nielsen average of 6.5/15, good enough to finish 54th among 63 programs ranked last week -- if the Big Boys wanted to count Fox in, which they don't ...

"Werewolf" even finished second to NBC in the four-network competition Saturday during those two hours ...

Next Thursday will be Joan Lunden's last day on "Good Morning America" before she departs on maternity leave. She'll be replaced by Kathleen Sullivan as co-anchor with Charles Gibson ...

Fox Broadcasting announced yesterday that Don Ohlmeyer has been named executive producer of the 39th annual primetime Emmy awards ... which will air on the fledgling network the night of Sept. 20 ...

Ohlmeyer made his mark as a producer and director of ABC Sports coverage of the 1972 and 1976 Olympics. He was hired by NBC Sports for the top producing job in its coverage of the 1980 Summer Olympics, which was aborted when President Carter banned American participation. He produced the 1977 primetime Emmy awards for NBC ...

Two years later he formed his own production company. His 1983 movie, "Special Bulletin," won an Emmy ...

Fox outbid the three big networks earlier this year to win a three-year contract to carry the primetime Emmys ...