BRIAN WILLIAMS IS AN aviation buff, so he likes to use an analogy about the gaze-narrowing hood worn during flight training to explain his singular focus on the “NBC Nightly News” — blocking out matters beyond his control, which range from the fading challenge posed by Katie Couric to NBC’s primetime fortunes.

“We have to stick to our knitting,” he says.

The anchor is probably wise not to peer too deeply into the periphery, because even at NBC, the news purist in him won’t care for what he finds.

Despite all the talk and tumult surrounding Couric’s jump from NBC to CBS, the evening newscasts have surely waned in importance from a bottom-line standpoint, eclipsed by the morning programs, which by virtue of sheer tonnage — those three hours of “Today” to peddle daily — have become massive profit centers. Hell, even Mel Gibson’s latest apology came on “Good Morning America,” not primetime.

Yet even if the chairs Rather, Jennings and Brokaw long occupied yield less gold, as the news becomes tarnished and tabloid-ized around them, they increasingly represent TV’s journalistic gold standard.

Nowhere is this truer than NBC, where Williams presides over a stately, globally aware broadcast that reflects the years he spent as Tom Brokaw’s understudy. At the same time, primetime newsmag “Dateline” and ABC’s counterparts have responded to a scary world by turning inward, becoming preoccupied with predators and salacious crime; “Nightline” has taken a stupid pill; and NBC’s morning jewel has become even giddier and less substantial, hard as that is to imagine, with the baton pass to Meredith Vieira.

That Williams enjoys seniority six weeks short of his second anniversary speaks to the turmoil evening news has endured, following two decades of Mt. Rushmore-like stability. But it’s not only the nightly news that has undergone a makeover.

The house Roone Arledge built at ABC News has shifted from a mix of high and low to a heavy emphasis on the latter, pushing “20/20″ and “Primetime” in that direction and revamping “Nightline” in a manner that truly is, to quote one of its more annoying new features, a “sign of the times.”

As for Couric, the trajectory of her personality-driven leap to CBS has proven strangely predictable: enormous initial curiosity followed by a dawning realization there’s not much “there” there — a point starkly underscored by her “How does one go about asking the secretary of state out on a date?” interview with Condoleezza Rice on “60 Minutes.”

Small wonder so many who sampled Couric’s “CBS Evening News” since abandoned it, leaving her with 7 million viewers during the Oct. 2-6 week — 1.6 million behind front-running NBC, and back in the third-place hole Dan Rather and Bob Schieffer occupied.

CBS will undoubtedly tinker with the broadcast, but playing to Couric’s strengths will only make it softer. Indeed, Rice’s return to discuss the North Korean crisis last week underscored Couric’s limitations when interviewing world leaders as opposed to lead singers and movie stars.

That places pressure to hold the journalistic line on Williams and ABC’s Charles Gibson — who peculiarly groused about the ads that air during his program to the Philadelphia Inquirer. Seriously, dude, ABC could run spots for “Mortal Kombat” and “Grand Theft Auto” and the “World News” audience would still skew old.

Given that Gibson is a stopgap anchor after ABC’s extraordinary string of bad luck, the best hope is thus Williams, who spruced up the place with his own blog and other online accoutrements but ultimately remains a throwback. Stylistically, “Nightly News” mirrors a newspaper front page with the requisite feel-good garnishes, delivered in that unflappable “voice of God” that’s received such a bad rap lately.

Mindful of this link, Williams’ office contains various reminders of broadcasting’s past, including a director’s chair signed by Walter Cronkite. He also displays a desk placard courtesy of the Truman Library that reads “The buck stops here”– indicating that he takes his managing editor title seriously.

Having weathered the promotional waves from Hurricane Katie, Williams appears well positioned to carry the broadcast news standard until some whippersnapper is ready to elbow him toward retirement. Given the flying circus around him, though, he really should avoid looking up or down — much less left or right — so by all means, stay under that hood.

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