SEATTLE -- "WHAT A GREAT TIME TO SELL!!! YOUR PROPERTY MAY HAVE INCREASED $30,000 TO $40,000 LAST YEAR ALONE," screams the flier from a Puget Sound real estate broker. Its message is a far cry from the 1970s, when Boeing Co. was struggling and billboards asked the last person leaving Seattle to be sure to turn out the lights.

The Emerald City is hot. With national magazines proclaiming the Puget Sound region the best place in America to live and raise children, at least 50,000 immigrants from California and the East Coast flooded the area last year. Since 1960, the population of Seattle and surrounding King County has risen 70 percent to 1.5 million. Today, 2.5 million people now live in the four counties that make up the Puget Sound region, a number that is expected to reach 4.1 million by 2020.

A booming economy and the influx of newcomers have made this former outpost the place to be, and the problems associated with rapid growth have come with its new status.

Residents constantly swap stories about traffic, crime and housing. At a time when the housing market was falling apart in much of the country, the Seattle area experienced the nation's fastest rise in home prices last year and analysts expect sales to increase again in 1990. In some neighborhoods, prices are rising 2 percent a month, compared with annual 4 percent to 5 percent increases during the 1980s.

The rental market is equally hot. Despite three years of apartment construction, vacancy rates in all but a few neighborhoods have dropped below 4 percent and the price of the average Seattle apartment rose 5 percent during the last six months -- more than twice the local rate of inflation.

Not everyone is thrilled with the boom. Last spring, voters passed the Citizens' Alternative Plan imposing strict limits on office building in the downtown area. In August, the city council banned new con- struction in outlying areas in response to complaints about congestion. And a local newspaper columnist periodically writes tongue-in-cheek pieces about a movement he has created to "Keep the Bastards Out."

A good deal of the frustration is vented on Californians, who consider Seattle prices bargains compared with those in the Los Angeles and San Francisco areas. New arrivals from California and the East Coast have formed support groups to cope with the cold shoulder they sometimes receive from local residents.

Although mostly good-natured, the conflict demonstrates concern that the quality of life as Puget Sound residents have known it is disappearing. A poll conducted by the Seattle Times last fall, just a week before the city's mayoral election, found 53 percent of respondents believed Seattle had become a worse place to live.

"Growth continues to hit the Seattle area like a high-speed freight train," warns Issue Watch, a publication produced by the Municipal League. The newsletter's tone is hyperbolic, but rapid growth has pushed citizens and politicians to offer management strategies that might meet the growth train head-on. The Municipal League is sponsoring a series of forums with the theme "Can Our Northwest Character Survive Growth?" The governor appointed a Growth Management Commission, charged with producing a blueprint for managing growth.

At the same time, numerous groups are jockeying to produce plans for regional development. No sooner had the legislature passed the Growth Management Act requiring regional planning for most of the state's counties and cities than a group called Citizens for Balanced Growth proposed an initiative that would repeal the legislation and impose stricter limitations on growth.

The current expansion began in the fall of 1983, when Boeing's work force in the state bottomed out at about 57,000. The recovery gained momentum over the next three years, receiving a strong boost from a lower dollar in 1985. Since then, Washington's economy has created new jobs at a faster rate than the national average. Over the past five years, the state added 384,000 people to the work force, bringing the total to 2.3 million. Of the 80,000 new jobs created each year, 60 percent are concentrated in the Puget Sound area.

The Washington State Employment Security Department reports that wage and salary employment grew 5.3 percent in 1989, the largest percentage gain since 1978. In a report recently released by the Federal Bureau of Labor Statistics, Washington State moved from 18th to third place in non-farm payroll employment growth.

Despite the finger-pointing at Californians and New Yorkers, a good deal of the credit, or blame, for the economy's expansion, lies at the door of the state's largest employer, Boeing.

The aerospace company had a record-setting year in 1989: profits of $973 million and 887 jet orders worth $46.7 billion. Boeing employment in Washington has risen 87 percent since 1983 to more than 106,000. Production has more than doubled from 12 planes a month in 1984 to 27. The orders have continued to roll in during 1990 and at its current production rate, it would take Boeing six years to deliver its backlog of planes.

While Boeing led the economic rebound, an expanding high-technology sector, a burgeoning service industry and strong international trade have also bolstered the recovery. Aerospace, software and biotechnology companies now employ one of every 10 non-farm wage earners in the state, according to the Employment Security Department.

Excluding Boeing, overall job growth in the high-tech industry averaged 14 percent in 1988 and overall statewide employment rose 4.7 percent. Even without Boeing, the high-tech sector is bigger than the state's lumber industry, which employed 41,000 last year, or the next largest industrial sector -- food processing -- which provided 31,000 jobs. A survey last winter by the New York accounting firm of Ernst & Young found that the Puget Sound area is the nation's seventh-largest center for commercial biotechnology.

The software industry is the fastest growing of the high-tech industries and the region's jewel is Microsoft Corp., the largest microcomputer software developer in the United States. Analysts predict Microsoft will have sales of over $1 billion and will employ 5,000 people in 1990. Where just 15 years ago Washington's software industry employed 88, it now boasts more than 19,000, making the state third in the country in software employment.

There are signs, nevertheless, that the region is beginning to feel the impact of a slowing national economy. Aerospace employment has fallen for two months. A survey of the top executives at small- and medium-size firms throughout the region conducted in May by Marple's Business Newsletter reveals continued strong business activity, but it also detected a clear undertone of concern. Orders are slowing and executives are worried about the shortage of skilled labor.

In addition, in contrast to rapid growth in the number of jobs, the Census Bureau reported in March that Washington income growth lagged behind that of most other states during the past decade. Per capita income rose 50.9 percent from 1979, but 38 states grew at a faster rate, pushing the state's ranking down to 19th in the nation from eighth in 1979.

In addition, the growth that has occurred has been uneven, creating two Washingtons -- the prosperous Puget Sound region, where average personal income is one-third higher than the statewide average, and the "other Washington," the 21 of the state's 39 counties outside the central Puget Sound Basin that are stagnant or declining.