Tom Shales On TV is a new weekly column by the Pulitzer-winning critic. He'll write not only on all things television but also about our culture and the forces that shape it. Look for him on Tuesdays.

One worrisome thing about "The Tonight Show" with Conan O'Brien is that the people who put it together don't appear to be worried. Maybe they're putting up a brave front or a happy face, but from the way they talk, you'd almost think the ratings were ducky.

When I dropped by during a recent trip to Los Angeles, life backstage at O'Brien's lavishly outfitted new studio reflected the standard pandemonium that comes with getting any TV show on the air. O'Brien flew by the greenroom with his tie untied and his shirt untucked, looking his boyish, pasty and anemic self. A happy sort of chaos prevailed in what might be called The Cone-Zone.

When I offered my congratulations, however, I got a more rueful than giddy smile. "I'm not sure congratulations are in order," he said, but good-naturedly. In fact, he is to be congratulated for how the show has been going -- it's nothing if not lively and laugh-packed -- but not, of course and alas, for how it's been doing in the ratings. After a walloping good start in June, the ratings plunged into the fruit cellar. Now, it's typical for O'Brien's NBC show to come in third, after CBS's "Late Show With David Letterman" and ABC's war-horsy "Nightline."

The situation is complicated by the fact that O'Brien has long been an admirer of the persnickety Letterman's; Dave even made an appearance on O'Brien's "Late Night" show long after Dave had gone to CBS. "Late Night" was, of course, Letterman's old stamping ground, and what influential stamping it was. Letterman's picture was posted on a wall of O'Brien's New York set, near late-night comedy gods Johnny Carson and Jack Paar.

Letterman "changed" when he went from 12:35 a.m. to 11:35 p.m., and O'Brien changed, too. He tidied up. The show is less bizarre-o, the comedy less eclectic and surreal. The props and costumes and even the graphics are slicker and have less of a homemade feel. Some of this is inevitable; there are many more viewers to please an hour earlier, and they are less likely to find self-mocking tackiness to be cute and amusing.

The obvious dilemma: You change too much, you're no longer Conan and you alienate your fan base. Change too little and older viewers may find the show too cuckoo and silly.

Anyone who's a fan of both comics, and it's easy to be just that, has a hard time deciding not only which to watch but also whom to root for. Both shows can succeed -- there are plenty of viewers to go around, and a great show will lure back expatriates who've wandered off to cable or to recordings they've made of prime-time shows they missed. Still, it's hard to conceive of any race without a loser.

If only they could take turns -- Letterman winning one week, O'Brien the next. NBC always says that O'Brien has the best demographics in late night, a solid following of viewers in the 18-to-34 range, but that's victory with an asterisk. Scorekeepers still like as many bodies as possible, even though in Madison Avenue's view if you're over 55, you might as well be dead.

Television, thou cruel mistress! O'Brien has just returned from a week's vacation during which, his producer Jeff Ross insists, little tinkering needed to be done and scant thought given to changes. That doesn't sound realistic, but the worst thing to do would be to go into panic mode (that's what network executives do). As Jay Leno himself recently noted, he had a rough time in the ratings during his first year as well, then went on to reign supreme for 16 years.

What, if anything, is Conan doing wrong? One of Leno's producers helped cure Leno's weak early ratings by warming him up -- that is, bringing the host and the studio audience physically closer to each other, and introducing the ridiculously corny gimmick of having Jay shake hands with a gaggle of pre-selected audience members while the rest of the crowd joined in a strangely mandatory standing ovation.

O'Brien might need warming up, too. He looks oddly lonely out on that enormous set with bandleader Max Weinberg and sidekick Andy Richter each so far away (though Johnny Carson wasn't much closer to Ed McMahon and Doc Severinsen).