Three major network television stations -- NBC, CBS and ABC -- have provided news and entertainment to American television viewers for decades. Each network broadcasts the evening news at 6:30, and for many American families, gathering around the television set to watch NBC anchor Tom Brokaw, CBS anchor Dan Rather, or ABC anchor Peter Jennings has become a tradition. But some media experts say that era may be coming to an end, with the retirement of NBC news anchor Tom Brokaw on December 1 after more than forty years on the air, and the recent announcement by CBS anchor Dan Rather that he plans to step down early next year. Kerry Sheridan has this story from New York.

"Good evening! Live from the Berlin wall on the most historic night in this wall's history…"

Tom Brokaw was the only Western news anchor to broadcast live at the Berlin Wall on November 9th, 1989.

"We have a remarkable development here tonight at the Brandenburg gate. On the other side, East Germans have now come to the wall and many of them have been seen crawling up on the wall being helped across by West Germans from this side."

Television news historian Jeff Alan says much of the public relied on Mr. Brokaw for key news events because his passion for the news was clear to see.

"When he was standing at the Berlin wall, when that Berlin Wall came down, he felt it. He felt every bit of passion that those people were feeling, who had been living for years and years and years under that rule there, and it had a profound impact on his life. And you could tell in his reporting. You can see that he really, really lived the journalism."

It was just one of many prominent news events Mr. Brokaw covered. A native of South Dakota, Mr. Brokaw started his career in 1962 in Omaha, Nebraska. He later covered news from both the West and East Coasts of the United States, serving as a reporter and anchor in Los Angeles, then as a White House reporter for NBC.

Mr. Brokaw began anchoring the NBC morning Today Show in 1976, and moved to the NBC Nightly News in 1982. His face and his voice have become instantly recognizable to millions of Americans.

"Well, when I was younger I always thought he was the best looking anchor!"

Gloria Lyndaker from North Carolina is touring New York City, and has stopped by the NBC studio at Rockefeller Center for a glimpse of the morning show celebrities. She says she grew up watching Mr. Brokaw on the news.

"At first I didn't particularly like his style but then as I watched more and more, I really believed and could trust what he was saying. And I would rather watch him than a lot of others."

Mr. Brokaw has spent much of his career traveling around the world to bring news home to American viewers.

"Good evening from Beijing. Two portraits of China tonight. This one where millions of Chinese are going about their daily routines. The other is more difficult to show: China as a police state."

In one memorable broadcast just hours after the 1989 massacre at Tiananmen Square ended, Mr. Brokaw and a small TV crew rode their bikes through the streets of Beijing. Using a hidden camera concealed on one of the bikes, the crew showed Americans their first view of the Beijing streets after thousands of protesters were killed or injured in violent clashes with Chinese government forces.

Mr. Brokaw also covered the Vietnam war, the Watergate scandal, and the spread of the AIDS epidemic.

"The news is difficult to absorb even as we report it. Magic Johnson has tested positive for the H-I-V virus."

When Mr. Brokaw took over as the sole anchor of the NBC Nightly News in 1983, he led one of three network news broadcasts -- the others were CBS and ABC -- that were the most popular source of evening news for close to 29 million people, or about a third of the estimated television viewing audience according to Nielsen Media Research.

Mr. Alan, the news historian, wrote a book about the television news anchors that have shaped American media. He says the networks' place in the American home is not what it used to be.

"In 1982, when Tom Brokaw, Dan Rather and Peter Jennings took over those three chairs at the three networks and were doing nightly news broadcasts, there were no remote controls sold with every television set and there was no cable news other than CNN which was less than a year old at the time. So people had to literally get up, walk across the room, change the channel to turn on a different station."

Now, the public has more choices for news. Cable channels such as CNN, MSNBC and Fox News provide 24-hour news coverage, and the Internet makes updated news accessible any time of day.

Analyst Bob Steele of the Poynter Institute, which focuses on educating future journalists, says the retirements of Mr. Brokaw and CBS anchor Dan Rather will be remembered as milestones in the history of television journalism.

"When you have two of the three traditional broadcast network anchors stepping down at approximately the same time, there is a kind of a benchmark moment. The audience has been diminishing for the particular broadcast networks in recent years. I don't think that has anything to do with Brokaw, Rather and Jennings as much as it has to do with the technological and marketplace changes: cable news as a very viable competitor and also the changing society in which we live. The opportunity for viewers to tune to not just several, not just dozens, but literally hundreds of different channels on television."

But ratings show that even as network news viewership is slightly down, it continues to draw a major part of the prime time television audience. For instance, CNN and Fox News combined draw about two-point-seven million evening viewers. NBC, CBS and ABC combine to draw about 26 million viewers.

In an NBC broadcast commemorating his 40-year-career in news, Mr. Brokaw recalled the major news events that shaped his life. One of the most recent was broadcasting live from New York the night of September 11th, 2001.

"It is one of the darkest days in America as we realize that this country has been attacked in an act of terrorist war in the heart of the nation's capital in Washington, DC, and also in New York City, and then a plane that was driven into the ground outside of Pittsburgh. We believe that is the end of the attacks for now but no one is sure because we don't know who is responsible."

"My emotions are pretty close to the surface, and that day I remember thinking, 'Don't lose control.'"

Mr. Brokaw is the author of three bestselling books, and he says he plans to work on documentary projects for NBC after he retires.