Low ratings and high production costs have pushed NBC's Tonight show with Jay Leno into the red, the New York Post reported today (Friday), citing unnamed insiders. "Leno May Be Next," the newspaper said in a headline, suggeSting that Comcast may replace Leno once it gains control of NBC Universal later this year. "You can't figure they're happy about this," said the newspaper's source. Ratings for Tonight have fallen below those that Conan O'Brien garnered when he hosted last year. Moreover, the network is shelling out considerably more money for Leno than it did for O'Brien -- $30 million per year vs. O'Brien's $15 million, according to the newspaper, plus the cost of a bigger production staff. What's more, the Tonight show, whose audience is down 20 percent since Leno left the show a year ago, has been overtaken in the ratings by the ABC newsmagazine Nightline at 11 30 p.m., and Tonight's ratings appear to have only one way to go once O'Brien enters the late-night fray in the fall. Meanwhile, David Letterman's ratings remain virtually flat with last year, which, commented the website TVbytheNumbers.com, "is pretty good in the broadcast television world where 'flat is the new up.'" Letterman's network, CBS, boasted in a news release on Thursday that Letterman's Late Show "delivered its most competitive second quarter against The Tonight Show in viewers and key demographics since 1995.