For some mall owners, negotiating loan extensions or refinancing may be difficult. Lenders are tightening their purse strings as unease surrounding the future of shopping centers grows, with bleak earnings forecasts from retailers including Macy's Inc. and Nordstrom Inc., and bankruptcy filings by chains such as Aeropostale Inc. and Sports Authority Inc. Older malls in small cities and towns are being hit hardest, squeezed by competition from both the Internet and newer, glitzier malls that draw wealthy shoppers.