ABC may have a final answer for its "Who Wants to Be a Millionaire" host Regis Philbin: Keep your day job. In a measure of how far the quiz show (that two years ago became an instant phenomenon) has fallen, network executives on Wednesday refused to guarantee that the game show will return to the air next fall. "We hope it will be, but we cannot say it with certainty," ABC Entertainment Chairman Lloyd Braun told TV reporters Wednesday. Overexposure is being blamed: "Millionaire" ran four times a week last season, and though ABC cut back to two nights this fall, a ratings slide continued. (Through mid-November, "Millionaire" was averaging 10.7 million viewers per episode, down 37 percent from the 17 million watching at the same point the year before.) Meanwhile, CBS had some happy news, some happy OLD news. Carol Burnett and Lucille Ball are not only TV's favorite redheads, but they are TV's all-time favorite performers, ratings-wise. This past Monday night's "The Carol Burnett Show: Show Stoppers" attracted nearly 30 million viewers, one of the biggest draws this season. (By comparison, CBS's Nov. 13 Michael Jackson concert special drew 26 million.) "It's amazing, just amazing," Burnett, 68, told The New York Times. The retrospective featured vintage outtakes from Burnett's 1967-78 variety show as well as newly taped reminiscences by Burnett, Harvey Korman, Tim Conway and Vicki Lawrence. Thanks in part to the Burnett special, CBS is expected to win the November prime-time "sweeps." Also contributing to the network's showing was the "I Love Lucy" golden anniversary special, more "comfort-food" fare that attracted nearly 18 million viewers Nov. 11.