THE traffic-clogged freeways that characterize the Puget Sound region during rush hour - one of which is Interstate 5, running from Tacoma to Everett - may get even more crowded in the years ahead if current growth projections prove correct.The region has witnessed phenomenal economic and population expansion in the past four or five years. Growth rates have now slowed, reflecting the impact of the recession. But according to a number of analysts, the region is expected to continue to expand, although at a slower pace. A disproportionate part of the state's overall economic growth is expected to occur in the Greater Seattle region, and especially to the immediate north and south of the city Seattle. "We're going to become one of the major economic centers in the Northwest," says Mayor Pete Kinch of Everett, just north of here. "We have several of the largest projects in the region underway here." The two largest projects for the Seattle-to-Everett region involve the expansion of Boeing Company facilities in Everett and development of a home port for the United States Navy. Snohomish County, north of Seattle, is already one of the fastest-growing counties in the state, if not the fastest growing; now, the Boeing/home port developments are expected to substantially boost population and add new wealth, according to Mayor Kinch. Most of the Boeing employees, however, will be people relocated from other Boeing plants around the state, rather than newly hired workers. Everett now has about 70,000 people. Mayor Kinch believes that the population will swell to 100,000 by the mid-1990s. And that isn't all: The other end of the Puget Sound area, directly south of Seattle, is also expected to post substantial growth in the next decade, according to Chang Mook Sohn, chief economist with the state Department of Revenue. Mr. Sohn says he believes that growth south of Seattle could be greater than that on the north side. Again, the expansion is centered around Boeing projects expected to be built in northern Pierce County, which is just south of Seattle and encompasses Tacoma. Mr. Sohn also sees "great potential in the Port of Tacoma," which has a larger land area than does the port of Seattle. In terms of trade volume, he says, Tacoma's port is now growing faster than Seattle's. Continued expansion is also expected east of Seattle, in the Bellevue area. Much of that development has been linked to the Microsoft Corporation, which is establishing offices throughout the Eastside region. Still, the overall economic growth here during the next few years will be only about half that of the late 1980s, Sohn says. Between 1986 and 1990, growth was running about 6 percent to 7 percent a year in terms of new job creation. But during the next few years job growth is expected to run about 3 percent a year for the region, he says. Robert Chase, research director for the Pacific Northwest Quarterly, an economic journal, also expects nonfarm job growth to be much slower, at around 3 to 3.5 percent next year. One of the main contributors to economic growth here during the past decade has been immigration. The immigration has been twofold: from other parts of the US, such as California, and from abroad, particularly from Asia. During the 1980s the state of Washington expanded from 4.1 million people to about 4.8 million - growing some 18 percent. But the really significant numbers involve various ethnic groups. The state's white population grew by only about 14 percent. According to Sohn, that growth was closely linked to economic cycles. Thus, the white population enlarged during good times and contracted during periods of recession. The black population grew faster, by 42 percent; Hispanics grew by 79 percent. But the Asian- American community grew by a whopping 106 percent. The Asian influx is not tied to changing economic conditions, says Sohn. The Asians come no matter what the underlying economic circumstances. Their influx has led to the revitalization of many parts of Puget Sound. The Asian-Americans have been entrepreneurial, creating small businesses.