ABC News president plans to launch a 24-hour news channel early in 1997 that its president, Roone Arledge, today claimed would be an alternative, rather than a challenger, to CNN. "It will be very difficult for ABC to put a dent in CNN's penetration because CNN has been around for so long," says senior media writer Richard Zoglin. "The fact that they have more than 200 affiliate stations will give them a leg up with local coverage, but the head start that Turner has may be insurmountable." ABC will seek to distribute the all-news programming using both cable and direct satellite, as well as new delivery systems developed by telephone companies. Last week, Australian media magnate Rupert Murdoch, complaining that CNN had become too liberal, announced that he too intended to start his own all-news network.