The Family Christian chain has filed for bankruptcy protection, saying that sales of its religious books, music and church supplies at its 266 retail stores have steadily fallen for years, Dow Jones Daily Bankruptcy Review reported yesterday. Officials who put the Michigan-based chain into chapter 11 protection on Wednesday said that they already have a buyer who promised to keep the 3,100-worker chain — which is one of the country's largest retailers of Christian products — open for business. Its stores are located in 36 states.