TUBE TALK In the post-Sept. 11 TV world, viewers have been eating up the comfort food of nostalgia programming. At CBS, where ''I Love Lucy'' and ''The Carol Burnett Show'' retrospectives have been ratings winners, network brass are talking to Burnett about doing even more specials. At NBC, they've been milking the 50th anniversary of ''Today'' (which finally arrives today) for at least a month, and they're planning a big prime-time blowout in May for the network's 75th anniversary. But ABC has missed two big recent opportunities to capitalize on its past. Producers of the TV movie ''Monday Night Mayhem,'' about the raucous early days of ABC's ''Monday Night Football'' 30 years ago, pitched the project to ABC and were rejected; the movie premieres tonight on TNT, where it will surely be played nearly as often ''Jaws'' and ''The Shawshank Redemption.''

ABC also turned down the producers of ''Roots: Celebrating 25 Years,'' a documentary paying tribute to the most popular and acclaimed miniseries of all time. ''They said, 'There's no audience for it. We don't think it's going to get an audience,''' says producer Judith Leonard. She took the project to NBC chief Jeff Zucker and says his reaction was ''not just, 'We'll do it,' but 'We're thrilled to do it.' He embraced it. I don't think the meeting took more than 15 minutes.'' The show will air Friday night on NBC, while ABC will be left to commemorate ''Roots'' during segments on ''Good Morning America.'' ABC honcho Lloyd Braun told TV critics at their Pasadena convention that Leonard's pitch was weak, but his brand new No. 2, Susan Lyne, took the blame for dropping the ball on the ''Roots'' special, saying that she and other ABC execs were too preoccupied by the network's current ratings free fall. ''If anybody should have suggested that to the network, fought for it, it's probably me, and I didn't think to do it,'' said Lyne, who, until last week, was in charge of miniseries and movies for ABC. Note to Lyne: There's still time to plan that 20th anniversary retrospective of ''Joanie Loves Chachi.''

Other news from ABC at the critics' confab: new shows ''Alias,'' ''According to Jim,'' and ''My Wife and Kids'' have been picked up for next season. Lyne says that, despite talk of its cancellation, ''Who Wants to Be a Millionaire'' will stay on the air and will get back to its roots with civilian guests instead of celebrities. Also, more than two years after Hugh Downs retired, Barbara Walters finally has a new cohost for ''20/20.'' It's John Miller, the ABC crime correspondent best known for landing an interview with Osama bin Laden back in the spring of 1998. Never having held a regular anchor job before, Miller says he was surprised to be asked. ''Actually, to take a page from Anne Heche, I thought I was from another planet when they told me,'' he says. ''But I have to fall back on my vast anchoring experience.''