SEATTLE — Nordstrom is not the only Seattle-based retailer to have gone national. Jay Jacobs Inc., a women's and men's apparel store, is expected to have some 300 stores in 20 states by the end of 1991, says Doris Williams, senior vice president. Listed on the NASDAQ market, Jacobs' stock rose 75 percent in the first quarter of this year.Unlike Nordstrom, Jay Jacobs looks for acquisitions. It recently bought "Up's N Downs," an apparel company in Sun Belt states. Typical Jay Jacobs' stores run about 3,500 square feet, compared to a Nordstrom store, which can run from around 70,000 to 350,000 square feet.