A rampaging Rottweiler fatally mauled two tiny, trembling pooches — one a champion show dog — in Central Park as their terrified owner watched helplessly. The grim episode unfolded late Thursday, as Melanie Coronetz, an Upper East Side author, walked her purebreds, Argo, 10, and his half-sister Monkey, 11, and a third mixed-breed dog just inside the park near 101st Street. As the dogs did their business, Coronetz said the hulking Rottweiler bounded out of the bushes and sank its teeth into them.