One of the small indignities of a high-paying television job is rising after getting home from Texas at 3:05 a.m. for a conversation about why your ratings are going south.

Brian Williams dutifully does it, weary voice and all, even if he and NBC can't fully explain why after two years on top his "Nightly News" broadcast has suddenly been eclipsed by ABC and Charles Gibson.

"It is predictable," Williams said, the morning after anchoring his newscast from Fort Worth. "This is why I haven't allowed any champagne toasts in the newsroom when the ratings have been flawless and spectacular and joyous. This is a back-and-forth dogfight."

Tough competition keeps everyone sharp and benefits the viewers, he said.

ABC's "World News" has been the most popular newscast for eight straight weeks, and 15 out of the last 19, according to Nielsen Media Research. Katie Couric's "CBS Evening News" is a distant third.

All the attention paid to Couric's tough start at CBS has overshadowed what's been going on at NBC. In Couric's first 39 weeks at CBS, she's lost 287,000 viewers from the average of a year ago, a drop of 4 percent from predecessor Bob Schieffer's audience. At the same time, "Nightly News" lost 533,000 viewers, or 5 percent, Nielsen said.

In Williams's first three months after taking over from Tom Brokaw in December 2004, "Nightly News" averaged 10.79 million viewers. In the past three months, it's been 7.66 million. To be fair, the nightly news audience traditionally drops when warm weather arrives, and it has been a slow news period.

Still, it's a lot of missing viewers.

"If I was at NBC, I'd really be quite nervous about the hundreds of thousands of people that have left my audience," said Andrew Tyndall, a consultant who studies the content of network evening newscasts.

Tyndall credits ABC more than he faults NBC. In a sense, the loss of audience NBC should have anticipated with Brokaw's departure was delayed for two years because of turmoil at ABC -- the death of Peter Jennings, injury to Bob Woodruff and departure of Elizabeth Vargas, he said. With Gibson, now there's stability.

Williams, whose "champagne toasts" comment was a sly reference to bottles passed around ABC's newsroom due to recent ratings triumphs, said he leaves it to others to worry about the numbers.

"I couldn't tell you what the ratings are and couldn't tell you that for days on end," he said. "It really is immaterial in a way. There isn't anything we can do on a given day to tweak."

If there was a single explanation, it would be much easier. There isn't.

A check of story logs from the past month reveals few dramatic differences between the ABC, NBC and CBS newscasts. The public can't detect much, either: a recent study by the Pew Research Center for the People & the Press found that 74 percent of people asked said ABC News, CBS News and NBC News are all pretty much the same.

The only major difference recently was that NBC led its newscast three times with hurricane-related stories, including a Williams visit to New Orleans and an update of the season's hurricane forecast. NBC's rivals did little or nothing on those stories. That's a reflection of Williams's continuing interest in the Hurricane Katrina aftermath, and he's convinced the public shares that.

NBC's prime-time ratings woes also may affect the visibility of its news programs and, more importantly, the local newscasts that are shown before Williams throughout the country. NBC is also fond of arguing the "Oprah factor," saying that when Oprah Winfrey has attention-getting programs -- primarily shown in the late afternoon on ABC stations -- it hurts "Nightly News."

"We worry about what we can worry about, but our numbers are affected by a variety of things we have very little to do with, nothing to do with," said Alexandra Wallace, a "Nightly" executive producer.

The simplest possible explanation, and toughest to deal with: more people want to spend that half hour with Gibson than Williams.

Gibson, 64, is an older man anchoring a news format favored by older viewers (Williams is 48). He's also more affable and self-effacing on the air, with less starch than the more formal Williams. Some see Williams as talking to, rather than with, his audience.

NBC has struggled to find a way to show, on the news, the warm, quick-witted Williams that appears in guest shots on "The Daily Show."

"Nightly News," under Wallace, has tried to showcase Williams more with occasional interview segments. Williams has conducted interviews with outgoing British Prime Minister Tony Blair and New York City Mayor Michael Bloomberg in the past month.

"Part of me does want the viewer to get to know Brian," Wallace said. "But I don't think that's the primary focus. The primary focus is putting on a journalistically sound, intelligent, well-rounded broadcast."