WASHINGTON, Sept 25 - Sales of existing U.S. homes rose 5.5 percent to a record pace in August, the National Association of Realtors said on Thursday. Sales of already owned homes climbed to a seasonally adjusted annual rate of 6.47 million units from a revised 6.13 million unit rate the month before. The number easily surpassed expectations of analysts polled by who forecast a rate of 6.05 million homes. The median sales price of pre-owned homes shrank to $177,500 in August, down 2.3 percent from the same month a year earlier.//