Poor sales have prompted a pair of popular retailers to close stores in Orange County. Barneys Inc., an upscale fashion chain based in New York, will close its store in South Coast Plaza on July 25. The chain, which still operates a unit in Beverly Hills, notified employees about two weeks ago of the change. Barneys filed for bankruptcy court protection in January 1996 over a dispute with Japan’s Isetan Co., which had financed the company’s expansion since 1990. Seattle-based Recreational Equipment Inc., a seller of outdoor gear, will close its store in Mission Viejo at the end of the year. Despite trying to revive sales for three years, “we weren’t able to get the kind of performance we needed,” said Michael Collins, a company spokesman. REI said it will attempt to find jobs in other locations for about 55 employees at the Mission Viejo store. The retailer, which also is shutting down a store in Utah, currently operates 51 stores in 21 states. It has five stores in Southern California, including one in Santa Ana, that will remain open. The privately held company operates as a co-op, with members paying a one-time fee and sharing in the profits.