There was a time when the Big Three network newscasts were virtually carbon copies of one another. No more. Unable to stem years of declining viewership for their flagship news programs, and looking at the prospect of a fall-off in advertising dollars, ABC, CBS and NBC are now locked in a struggle to stand out from the competition. If they can’t bring in new viewers, they’ll cannibalize the ones that are there.

A scant five years ago, the three network newscasts garnered a 60 share of the available audience. This season the combined number has dropped to a 56 share, even though the factors that took the initial bite out of their audience have been in place for years.

To date, all three have failed to stop the audience erosion that has plagued them since the rise over the last decade in the availability of national and international news to local newscasts, and the growth of a variety of news outlets, ranging from CNN and all-news radio to a raft of TV newsmags on the webs and in syndication.

“It’s been a long time since we’ve been the first source of information on the big stories of the day,” says Andrew Heyward, executive producer of “The CBS Evening News With Dan Rather and Connie Chung.”

“However, to a certain extent that’s freed us up to be more enterprising in what we cover. If you look at the lineup of the three evening newscasts now, once you get past O.J., there’s a real divergence in what each of us chooses to cover.”

News brass blame some of the decline this season on a slew of affiliate switches that have rocked the business, with CBS taking the biggest hit. But it’s all part of a viewer fallout that’s gone unabated for more than a decade.

The networks have compensated for any potential revenue loss from the ratings decline by adding additional commercials to their newscasts. Over the last two years, each has shoe-horned in approximately a minute more that their sales staffs can sell. But they’ve probably played that gambit to the hilt and now must figure out how to stop the audience erosion before they face a serious decline in revenues.

So now all three newscasts are struggling to redefine themselves, and the moves have caused a fair share of tumult at each shop.

At “CBS Evening News,” freshman executive producer Heyward, who took the reins in October, has tightened up the newscast, putting more of a focus on international news, as well as making moves to better define Rather’s and Chung’s roles.

Before Chung’s controversial “Eye to Eye” interview with Newt Gingrich’s mother, Heyward was dispatching her on assignments that previously would have gone to Rather, such as the signing of the Israel-Jordan peace accord.

In the wake of the Gingrich controversy, Chung was sent to cover the swearing in of the new Congress. Meanwhile, Rather has taken on the lion’s share of the O.J. anchor duties.

“The co-anchor format has greater potential than we’ve demonstrated so far,” says Heyward. “It can enable us to give weight to two big stories. It’s something that distinguishes us from the competition.”

Heyward may be a vocal champion of Chung, whom he worked with at “Eye to Eye,” and the dual anchor format, but inside the corridors of CBS News there’s talk that Chung’s anchor days may be numbered.

And even if the infamous Ma Gingrich “bitch” piece wasn’t the case of journalistic malfeasance some have made it out to be, it prompted a torrent of angry viewer letters to CBS and its affiliates, further weakening her position at the network

Much to the dismay of the news brass down the street at 30 Rock, “NBC Nightly News With Tom Brokaw” has yet to benefit from the internal turmoil at the competition. Nor has “Nightly News” been able to capitalize on the resurgence of the network’s primetime schedule and the relative health of its other news shows, including “Today” and the three editions of the newsmag “Dateline: NBC.”

Field trips

Says an NBC News veteran. “When (NBC News president) Andy Lack came in, he was eager to fix ‘Nightly.’ He brought in Jeff Gralnick to be executive producer from ABC, ostensibly to tighten up the show. Research showed that if we got Brokaw out into the field it would help strengthen ties with our affiliates and we’ve done that. We’ve also moved away from perhaps our greatest strength – our Washington bureau – and have put a lot more focus on stories from the hinter-land. Meanwhile, we’re doing appreciably less international coverage than the competition.”

One of the architects of “Nightly News’ ” move beyond the beltway is Brokaw himself. The anchor defends the strategy, even if it hasn’t translated into higher ratings, adding that because the newscast has more favorable demographics than CBS, it demands higher ad rates.

“We’re trying to do a newscast that’s more memorable than the competition,” Brokaw says. “We’re not going to become slaves of the Beltway. We’re going to continue to cover not only the changes under way in Washington, but how they affect people’s lives.”

If that’s the blueprint, NBC’s new resident pundit, Bill Moyers, will fit right in. Looking trim after bypass surgery nine months ago, Moyers seems ready to take the mantle of “NBC Nightly News” eminence grise. Lack has lured Moyers aboard with the hopes that adding a regular Moyers commentary to the mix will lift “Nightly” from last place in the network evening news race.

“Certainly one of the reasons I’m here is to differentiate NBC from the competition,” says Moyers. “It’s all part of the challenge of these newscasts: How do you make them relevant when there’s such an information overload out there?”

The appointment of Moyers has drawn heat from conservatives, who’ve targeted him in the past as a prime example of a so-called liberal bias at PBS, and from competitors at the other news divisions, who call him a fig leaf for a newscast that has gone soft.

But other veteran newsies remember that when Moyers became a commentator on the “CBS Evening News” in 1981, Rather had taken over the anchor chair from Walter Cronkite and the ratings had started heading south. The alchemy of news ratings is a strange thing, but shortly after Moyers started offering his views on the topics of the day, “Evening News” moved back into the top slot.

At the current top newscast, “ABC’s World News Tonight With Peter Jennings,” there’s a certain unease about who is in charge. Exec producer Rick Kaplan, who took over the helm a year ago after the quick firing of Emily Rooney, almost ankled a few months back for a job with Oprah Winfrey’s Harpo Prods.

ABC insiders say it’s a matter of time before the volatile Kaplan moves into an entertainment slot at the Alphabet web or with the net’s new studio partner, DreamWorks SKG.

“He has no immediate plans to do so, but Rick will leave in time and I’m sure when he does, we will be prepared,” says the ever-politic Jennings.

Meanwhile, “World News” is staying the course it charted for itself years ago, staking the up-market audience with more international news and less O.J. than its competition.

“It’s certainly a story you can’t ignore, but it’s been a conscious decision of ours not to be too swept up in the O.J. trial so it overwhelms what we’re doing,” says Jennings. “We’re going to stay serious with ‘World News’ from top to bottom.”