Calling recent urban renewal efforts 'a grave threat to the city's fragile rat population,' a group of New York City conservationists called for an end to the destruction of rat habitats Monday. 'The redevelopment of run-down, abandoned buildings in Times Square drove more than 240,000 rats from their natural habitats in 1997,' Rat Foundation director Mary Brinn said. In an effort to save the species, the Rat Foundation is demanding that eight city sewer lines be set aside as federally protected rat preserves. 