At the turn of the century, when the United States still was largely an eastern nation, historian Frederick Jackson Turner advanced the idea that it was the western edge of settlement that played the determining role in shaping American consciousness.

Writing at a time when western population was small and western influence peripheral in terms of national power, Turner found symbolic importance in the West. The West was the frontier, the safety valve, the place to which adventuring or disillusioned easterners could escape. Throughout the intervening generations, this mythic view of the West has endured.

Today, however, the West appears to stand on the verge of a decade in which its actual importance to the nation, in economic and demographic terms, will surpass any symbolic significance.

The West is the richest resources area of the nation, and the fastest growing in population.So western decisions on such issues as oil shale development, nuclear power, alternative energy exploration growth restriction are rapidly coming to have impact on the lives of all Americans.

Virtually every major political movement of the past decade - from environmentalism to Proposition 13 - has had its origin in the West. Keyed to such industries as aerospace and electronics, western employment has expanded steadily even at a time when job opportunites remain static in many other regions.

Since 1950, even through recessions, real personal per capita income in the West has been between 10 to 20 percent higher than in the northeastern, Plains and Great Lakes state. Last year, nonagricultural employment in the Pacific and Rocky Mountain states grew by more than five times the rate of most southern states. The economy of California, the West's megastate, increased at more than twice the national average.

Many top western economists expect these trends to continue. They see the West becoming wealthier as the East declines.

"Economic growth has to come for some tangible reason," says Perris Taylor, western regional manager for Data Resources, a Massachusetts-based economic forecasting company. "It isn't regulated by the government, it's regulated by resources - labor, land, minerals. As you look at those, the West has them all."

Taylor predicts that the eight Rocky Mountain states - Montana, Wyoming Colorado, Utah, Arizona, New Mexico, Nevada and Idaho - will continue to pace national growth.

Rich in natural beauty, which attracts new residents, and full of oil and coal, this region's growth in personal income exceeds the national average. While manufacturing jobs decreased nationally by more than 1 percent last year, they increased 4 percent in these mountain states.

Data Resources, founded by Harvard economist Otto Eckstein, predicts that personal income in the West will far outstrip other regions from 1978 to 1981 and that manufacturing will decrease in the industrial heart-land of America while expanding in energy-rich mountain states, Texas and the Pacific Coast.

Bank of America chief economist Walter Hoadley maintains that recessions, such as the one suffered by the United States in 1973-74, basically affect regions making expensive durable goods, such as automobiles and steel. Those industries are concentrated in midwestern and eastern states, and parts of the Deep South.

The one western industry badly hurt in earlier recessions - aerospace - seems largely immune to recession today. Aerospace companies have assured themselves of markets by contracting with foreign nations such as Japan. Many firms have at least two years of back orders.

Bowing, the Seattle-based aerospace giant whose slump once keyed a Northwest recession, is now doing so well that 12,000 workers were hired last year. California companies in the same field expanded their workforces by more than 25,000. Electronics firms - in Texas, Oregon and California's "Silicon Valley" south of San Francisco - also posted huge increases in employments.

"The country is lagging so far behind us," says Hoadley. "We're backing into a tremendous period of growth in the 1980's out here. The West has a lot of potential resources and a dynamism which simply doesn't exist back East."

Westerners are inclined to see this growth as a force that makes the region the national center of political change. As the West grows wealthier and more powerful, its disdain for the East and its seemingly decaying cities and stagnating industries sometimes borders on contempt.

"There is a cultural war going on in this country now between our past and our future," contends Gray Davis, chief of staff for California Gov. Edmund G. (Jerry) Brown Jr. "It's one coast against another. The West has learned from the mistakes of the East and that makes us stronger. People resent power, and power is now flowing to the West."

Davis' sense of the West's manifest destiny is, of course, tied to the political ambitions of his boss. But similar expressions of anti-Eastern, or anti-federal, jingoism are common-place these days among western politicians of all persuasions.

Celebrating an individualism that would make Horatio Alger blush, many westerners fail properly to acknowledge their debt to the rest of the nation or their frequent dependence on the central government. Western states continue to receive enormous federal subsidies for water development.

And the six western states (of 30 in the nation) that have passed resolutions calling for a balanced federal budget received more than $19 billion in federal funds last year.

While the reality of the West does not precisely square with its self-image of pioneering independence, the optimism that pervades much of the region is justified. More than anything else, it reflects a persistent pattern of western growth and the promise of more growth to come.

"The growth dynamism is what creates the dynamic for change," says Bank of America's Hoadley."Growth is necessary to change. When you grow you have to make choices about pollution and other problems which force you to change."

Some of the changes have included so-far inconclusive attempts to limit growth through retrictions on building permits, as has occurred in Petaluma, Calif., and Woodburn, Ore. In a far-reaching experiment, California has tried to regulate development and improve public access along its coastline.

The hostility encountered by the California Coastal Commission when it tried to carry out this voter-approved mandate of regulation demonstrated that the developmental urge is alive and well in the West.

Californians, said one bewildered former commissioner, seemed to want preservation and development of their coast simultaneously. These contradictory immpulses are common throughout the West.

In such western states as Utah and Wyoming, the dominant idea appears to be a belief that the energy crisis has provided a golden opportunity.

"There's a mentality in Utah that the future is in energy," says Paul Parker, a state planner. "There's going to be an energy crisis and we are going to capitalize on it."

At the same time, westerners have taken the lead in conservation and experimental use of resources.

"Literally, the West is where the frontier enden and frontier mentality began to end," says Bill Press, director of California's department of planning and research. "This is where the environmental movement started because we became the first to realize that resources were limited."

This awarness of limits was vividly demonstrated in Los Angeles during the drought that ended last year. Although the city's water supplies were ample, an appeal for water conservation to help hard-hit northern California succeeded beyond everyone's wildest expectations.

Phil Hawley, a Los Angeles corporate executive who headed a conservation task force, suggested that the city try a 10 percent water reduction enforced by surcharges on those who would not comply.

But few surcharges were necessary. Los Angeles cut its water use by 17 percent, and Hawley now proposes that the "Los Angeles Plan" become the model for national energy conservation.

Such reponses to the "era of limits" proclaimed by Gov. Brown have not been limited to California. In the Pacific Northwest, a new generation that is skeptical of nuclear power and determined to maintain the area's environment has embraced the values of conservation.

Three years ago, for instance, Seattle City Light ditched plans for nuclear power plants and launched an energy conservation effort that kept growth in energy use two percentage points below projections.

"People that live here are in love with this city and want to keep it a great place to live," says Peter Henault, environmental affairs directior at City Light. "We thought conservation was a lot cheaper, a lot less environmentally harmful and just made more sense.It's turned out, everyone now agrees, to be a pretty demned good decision,"

Similar innovative approaches have occured in Oregon, which as long as 1975 began granting 25 percent tax credits for wind, solar and geothermal development. Portland General Electric has agreed to buy back, at its own rates, electricity produced by home solar and other generation. Some Oregonians are building small hydroelectric generating facilities, while more than a tenth of the state's residents now use wood as their chief source of fuel.

Whether such incremental approaches to environmental protection will withstand the coming push of development in the West is open to guestion.

Oregonians are already complaining about the steady population pressure and increasing pollution in such areas as the Willamette Valley. In Colorado, six oil shade plants are on the drawing boards, any one of them a bigger strip-mining operation than all of the mining done in the state during two decades of a mining boom that ended in 1890.

In Montana, huge coal-burning electric plants pollute once-pristine air, and environmentalists are on the defensive in legal efforts to prevent further development.

Can the West control its development and preserve the best of its resources as it rushes headlong to become the economically dominant region of the nation? $ That question remains unanswered in the West, as the region embarks on a simultaneous era of limits and development. If historian Turner were still around, he might find it a challenge equal to settlement of the frontier. CAPTION: Picture 1, An aerial view of land in Maricopa County, Ariz., showing the encroachment of urban growth onto agricultural land at Phoenix. Westerners see such growth as making the region a national center. Photos by John McDonnell - The Washington Post; Picture 2, A Central Arizona Water Project pipeline tunnel - symbolic of the West's dependence on federal water subsidies.; Picture 3, Twin shafts of shale mine near Rifle, Colo., part of the energy potential.