ABC, CBS and NBC could lose a combined $ 15 million in advertising revenue due to the four 90-minute political debates, which will preempt such hit shows as “Full House,”"Cheers” and “60 Minutes.”Although none of the networks gave a loss prediction, one network official called the $ 15 million figure “not too far off target.” Accompanying financial losses will be sustained by many local affiliates as well, which for two of the debates will preempt programming in the “prime access” period at 7 p.m. EDT, when lucrative syndicated shows are usually aired. Additional headaches for CBS could arise from conflicts with its must-air live coverage of the Major League Baseball divisional playoffs. For instance, the kickoff debate Sunday at 7 p.m. EDT is wedged between two playoff games, with the first starting at 4 p.m. EDT. In addition, there could be a conflict if the American League playoffs go to a seventh game the following Thursday, when the second presidential debate is to begin a half-hour later. The schedule for the presidential debates is: Sunday, Oct. 11, at 7 p.m. EDT; Thursday, Oct. 15, at 9 p.m.; and Monday, Oct. 19 at 9 p.m., in, respectively, St. Louis, Richmond, Va., and East Lansing, Mich. The vice presidential debate takes place in Atlanta at 7 p.m. on Tuesday, Oct. 13. Although the debates come at the beginning of a new TV season, most of the preemptions will be of established shows, not new fare, and should have no lasting impact, according to David Poltrack, VP of research and planning at CBS. Overall, “The effect from viewer disruption shouldn’t be very severe, and seems to be pretty balanced” across the three networks, Poltrack said. During the concentrated lineup of debates, the Big Three will likely lose viewers to other channels counterprogramming with entertainment shows.