New York ? It’s tempting to write off broadcast network evening news programs as relics of another time.

The three evening news shows, which once commanded three-quarters of the TV audience, now claim less than half. Morning shows and cable news are eating away at their relevancy, and their audiences are aging.

Tom Brokaw, Peter Jennings and Dan Rather, each an evening news anchor for two decades, are all nearing or past normal retirement age.

And ABC’s recent attempt to replace “Nightline” anchor Ted Koppel with David Letterman provided fresh evidence that the giant media companies that own TV networks aren’t afraid to threaten news institutions if they see a compelling business interest.

Is a giant tree in the television news business ready to fall?

Don’t hold your breath. It would be a mistake to conclude that NBC’s “Nightly News,” ABC’s “World News Tonight” or the “CBS Evening News” are headed for extinction soon  even when their current anchors step down.

Simply put, the long-term harm to the networks’ owners is likely to outweigh any short-term financial benefit that could be gained by replacing the news with more profitable programming.

And although it’s too early to tell whether the steady decline in viewership has ended, more people are actually watching these programs this year than last.

“My view is that the genre is alive and well,” said Steve Capus, executive producer of “Nightly News.” “What all three of us do is provide an extremely valuable service to the American audience, and I think that’s going to be in demand for a long time to come.”

Fighting for audiences

The three shows are certainly as competitive as ever. Brokaw and Jennings traveled late last month to the Middle East for the Arab Summit. Rather came a week later  and his producer chided ABC and NBC in print for sending their anchors home when warfare spun out of control.

The need for a 22-minute summary of the day’s news would seem an anachronism now that CNN, Fox News Channel, MSNBC and the Internet all offer news instantly. According to a survey by the Pew Research Center last fall, 53 percent of viewers said cable was their main source of TV news.

Yet each weeknight, more than 31 million people watch a network evening news program. The most popular cable news program, Fox’s “The O’Reilly Factor,” typically draws nearly 2.1 million viewers a night.

Evening news producers say the existence of cable news has forced them to add depth and context, partly in contrast to the breathless “news as it happens” style of cable during the day.

“I always appreciate that we live in a universe with a lot of information,” said Paul Slavin, executive producer of “World News Tonight.”

Profits and perspective

The networks’ advantage in offering perspective was on display after Sept. 11, said Frank Sesno, a former CNN Washington bureau chief who now teaches at George Mason University.

“I worked for CNN,” Sesno said, “but I watched the networks every night.”

All of the evening news programs say they are profitable. It’s difficult to isolate what is spent on each, because an evening news reporter could also file stories for other broadcasts. In NBC’s case, they can file for sister networks MSNBC and CNBC.

Still, there’s little question that networks could save money by filling the time slot with game shows or entertainment news instead.

Many analysts say the uproar wouldn’t be worth it.

The networks’ corporate owners  General Electric for NBC, Viacom for CBS and the Walt Disney Co. for ABC  all are big players in Washington who frequently seek beneficial legislation or Federal Communications Commission rulings. Eliminating the evening news would damage their arguments that TV networks serve the public interest, Wolzien said.

Sesno agreed. “From a public-relations point of view and a corporate citizenship point of view, it would be colossally difficult, if not impossible, for any of the networks to dump an evening news broadcast at this point,” he said.

Two of the three anchors  Brokaw and Jennings  face big decisions about their futures with contracts expiring this year.

Although, Brokaw, 62, is the youngest of the trio, he has mused loudest about leaving. He took most of last summer off, but was rejuvenated by the searing news events since then.

The ability and willingness of ABC to pay Jennings, 63, is being watched carefully. The network is struggling financially.

ABC, however, has seen the largest increase in viewership over the past year of the three shows. “World News Tonight” generally ranks second each week to NBC.

Rather, 70, is last in the ratings. But he’s given no indication he’s anxious to leave, and he arguably dominates his news division more than the others do.