Tired of neighborhood decay, upset about criminal tenants and absentee landlords, and burnt by a rash of fires, Pittsburgh Council members yesterday called for enforcement of a law on nuisance properties passed almost two years ago but so far ignored. The ordinance allows the city to bill owners of problem properties for the costs associated with policing and inspecting them. "We've internally, since I've become mayor, looked at that," said Mayor Luke Ravenstahl, adding that enforcement may be on the way. "We're just not there yet. It takes cooperation between a number of city agencies."