When Debbie Parkhurst choked on a piece of apple at her Maryland home, her dog jumped in, landing hard on her chest and forcing the morsel to pop out of her throat. When the Keesling family of Indiana was about to be overcome by carbon monoxide, their cat clawed at wife Cathy's hair until she woke up and called for help. For their nick-of-time acts, Toby, a 2Â½-year-old golden retriever, and Winnie, a gray-eyed American shorthair, were named Dog and Cat of the Year by the American Society for the Prevention of Cruelty to Animals. In addition, five humans were honored Thursday for their actions toward animals in the past year, including a Bronx firefighter who saved a dog and cat from a burning building. Neither Parkhurst nor Keesling could explain their pets' timely heroics, though Parkhurst suggested her pooch's Heimlich maneuver might have been guided by divine intervention. ''That's what our veterinarian said,'' she said. ''He wasn't making a joke; he's very spiritual, and now I have to agree with him.'' Both pets were themselves rescued in infancy _ Toby as a 4-week-old puppy tossed into a garbage bin to die, and Winnie as a week-old orphan hiding under a barn, so helpless that Keesling's husband, Eric, had to feed her milk with an eyedropper. As the Keeslings recalled it, a gas-driven pump being used to remove flood waters from their basement in New Castle, Ind., last March malfunctioned, spreading carbon monoxide through the house. By the time Winnie moved into rescue mode, the couple's 14-year-old son, Michael, was already unconscious. ''Winnie jumped on the bed and was clawing at me, with a kind of angry meow,'' Cathy Keesling said. ''When I woke up I felt like a T-bar had hit me across the head.'' State police and sheriff's officers responding to her 911 call said the family was only minutes from death, judging by the amount of poisonous gas in the house. Debbie Parkhurst's husband, Kevin, was at his job at a Wilmington, Del., chemical firm when she took a midday break from making jewelry and bit into an apple. ''Normally I peel them, but I read in Good Housekeeping magazine that the skin has all the nutrients, so I ate the skin, and that's what caused me to choke,'' she recalled. ''I couldn't breathe and I was in panic when Toby jumped on me. He never does that, but he did, and saved my life.'' Both Toby and Winnie accompanied their owners to the awards luncheon at Manhattan's posh Rainbow Room atop Rockefeller Center.