TRENTON Following the shooting of two black bears that wandered into heavily populated communities this month, the national Humane Society has called on Gov. Jon S. Corzine to change a state policy that allows the killing of bears found in urban areas. On Wednesday, May 10 police killed a 300-pound bear cornered in a small backyard in Irvington. Officers said the bear reared up and appeared ready to charge them. That bear shooting came only days after a 225-pound bear was caught in downtown Trenton, prompting state biologists to kill it. It was the first time a bear had been killed as part of the state’s no-tolerance policy on bears found in densely populated areas.