SEATTLE - Retailers in the Pacific Northwest are coping this week with the loss of part of a major interstate due to flooding resulting from heavy rains. A 20-mile stretch of Interstate 5 - the road that connects Seattle with Portland - was shut down Monday and had not opened by late yesterday, requiring drivers trying to get from one city to the other or points in between to take a 450-mile detour. That situation is resulting in significant distribution delays, a spokesman here for the local division of Unified Grocers, Los Angeles (formerly Associated Grocers, Seattle), told SN yesterday. "But we're playing the hand we've been dealt," he said, "and letting our members know they can expect delays of up to several hours - for example, a delivery that normally comes in at midnight may come in between 4 a.m. and 5 a.m." Although a handful of memeber stores may be closed due to flooding at store level - "and while some have told us not to schedule any deliveries until they tell us we can get to them," he added - most stores were operating fairly normally, the spokesman said. The interstate was supposed to re-open today, he noted.