New York ? Bob Wright, the chairman of NBC Universal, has a theory about his prize employee, Brian Williams, who tonight will become the face of the United States’ top-rated newscast.

“Early on in his broadcast career,” Wright mused recently, “somebody sat him down and said, ‘If you don’t act serious all the time, people won’t take you seriously.’ And that gave him a picture of himself in the back of his mind.”

Here’s the picture, off camera: Williams as cutup, devastatingly accurate mimic, former volunteer firefighter, NASCAR fan. On camera, though, dressed in his impeccable suits, he looks more like the conventionally handsome, button-down guy central casting dispatched to play an old-school role — anchorman.

Williams has heard it all before and takes a certain perverse pride in his decorous style. “If you want loose, there’s plenty of that” elsewhere on TV, he said. “If I have a fault, it’s probably too many years of Catholic school training. I have still — whether I am electronically or physically invited into someone’s home — a notion of how I should behave. So I wear a tie to work, and I usually treat it with some seriousness when people invite me into their home. And look, post-9-11, most of what we do in these broadcasts is so ungodly serious these days, I’m willing to be called an anachronism if propriety is the charge.”

Still, as the first network in two decades to make a major anchor change, NBC is hoping it can position Williams as someone able, as Wright puts it, to “connect to people at all kinds of levels.” It’s one of the main challenges the network faces as it manages the tricky transition at “NBC Nightly News,” following Tom Brokaw’s decision to step down after 21 years in the role.

Among the broadcast networks, NBC’s evening newscast is the leader, pulling in an average 9.8 million viewers per night and estimated revenues of just over $100 million this calendar year. So in the last couple of years, Williams has been attending a finishing school of sorts.

Although he was already a seasoned reporter and anchor with the difficult White House beat and a nightly cable newscast under his belt, he still had some ground to cover.

In 1999, a New York Post TV critic quoted Williams as saying on MSNBC, during a report on the Columbine High School massacre: “We should tell you that we are approaching 9:15 on the East Coast, 6:15 on the West Coast, on a day that follows one and precedes another, a day that is filled with 24 hours, each hour seeming like so many more. …” And that was just for starters. Williams talks more succinctly now.

He popped up around the globe, including a recent trip to cover Yasser Arafat’s funeral, as NBC sent him on a whirlwind of reporting assignments to give him the foreign experience he lacks. For a while, Williams was assigned to work with a veteran executive producer with four decades of experience in evening news.

And to soften his sometimes-too-serious demeanor, he’s been booked on late-night comedy programs and on “Imus in the Morning,” where he held his own even at 6:30 a.m. after a sleepless election night. “Brian is indeed charming and funny, so we’ve looked for more ways to show that,” said Neal Shapiro, the president of NBC News.

Part of Williams’ job will be to recruit viewers in his own age group, the ones who no longer have the evening newscast habit. He also has been lobbying behind the scenes to have the program rebroadcast each night at 7 on one of NBC’s cable channels.

On the cusp of attaining his dream job, Williams said that despite the hurdles, the post “still retains its allure and romance to me.” The job itself, as it came to be embodied in Brokaw, has more to it than reading the news each night: Brokaw threw his power around in the hiring and firing of news division executives and in lobbying network programmers to give more time to news events such as political conventions.

“It’s not just the day-to-day job; it’s what you come to mean to a news division,” Williams said. “I can’t wait to lead. This is the greatest staff ever assembled in television news.” But, he added, “Power comes to you when it’s earned over time.”