From the highrise office towers of this western financial capital to the rich wilderness lands of Alaska, Japan is building a new economic empire in the American West.

Japanese interests, enriched by a huge trading surplus with the United States and the skyrocketing value of their yen currency, are quietly buying billions of dollars' worth of western land, timber, fish, agricultural products and industrial facilities.

Close to half of Japan's almost $29 billion trade with the United States in 1977 went through western ports, where thousands of Japanese cars, televisions and other manufactured goods were exchanged for western minerals, timber and farm products.

Over the last decade in each of the five Pacific western states - Alaska, Hawaii, Oregon, Washington and California - Japan has emerged as both prime international trading partner and investor, establishing an economic sphere of influence unprecedented in the often-xenophobic West during recent times.

Many western business and government leaders are seeking to encourage this growing interdependence with Japan as a way to expand the already prospering economies of their states.

"We don't want to rely any more on the establishment of the eastern states. They're Europ-oriented, and our future is with Japan and the Pacific Rim," said Richard King, director of the newly established California Office of International Trade.

"The Japanese see California as part of their 'Pacific coprosperity sphere,' and we better be responsive to that," he said.

While sharing King's sentiments, many Japanese businessmen shy away from the "coprosperity sphere" label out of fear that some Americans might recall how that precise term was used by World War II Japanese militarists to justify their then-far-flung Pacific empire.

"But, of course, we do see it that way," said one smiling Japanese banker in San Francisco. "We see California already as part of Japan. Oh, yes, California Prefecture."

But the increasing power of Japan over the western economy is no laughing matter to others here - ranging from industrialists to labor union officials and native Americans - who fear that a quasi-colonial relationship is developing between the western states and the island nation.

They claim the West, in classic colonial fashion, is already surrendering its vital natural resources in exchange for much more costly manufactured products - a pattern which last year caused the western states to run up over a $3.6 billion deficit with Japan, twice the region's 1976 trade imbalance.

Kazutoshi Satta, manager of the San Francisco office of the mammoth Mitsui Trading Co. and director of the Northern California Japanese Chamber of Commerce, said he expects the present Japan-western states trading pattern to continue in the coming years.

With the exception of airplanes and maybe some canned foods, Satta said he believed western industries will have little chance of selling its finished products in Japan.

"Our processing industries are simply better than in the United States," said Satta, whose 300-year-old company has more than 140 trading offices in some 80 nations. "If the United States wants to sell us finished consumer products, they don't have a chance."

Japan's continuing reluctance to purchase American-manufactured goods makes some western business leaders fear their region may become a mere "resource colony" of an ever-expanding Japanese imperium.

"The question is whether we want to become a banana republic," said E. Floyd Kwamme, vice president of National Semi-Conductor, a large electronics manufacturer in Santa Clara, 40 miles south of San Francisco. "The problem is that manufacturing creates more jobs than agriculture. If we think we are trying to balance our trade imbalance with the Japanese by selling them beef and grapefruit, we'll end up killing our industrial base." The semiconductor industry, which makes the component parts for computers and other advanced electronic products, is one of a number of western industries, including lumber milling, fish processing, steel and autos (almost one-quarter of California's cars come from Japan, twice the national average), that are reeling from strong Japanese competition.

While American manufacturers still control 60 percent of the world's semi-conductor market, the industry has been singled out for domination by the Japanese industrial establishment, backed financially with government research money.

Already, enriched by the over 33 percent increase in the value of the yen since 1972, some Japanese semi-conductor companies are moving into places like Santa Clara's "silicone valley," perhaps the world's single most important concentration of high-technology industry, buying out small American firms, hiring skilled American engineers and, in the process, according to National's Kwamme, "picking for themselves the fruit of our technology."

At the same time, American semi-conductor executives complain that their products are being restricted on the Japanese home market by tough import regulations and alleged government-business collusion in Tokyo.

Japanese business leaders claim that their intrusion into the previously American-dominated semiconductor and computer industries is necessitated by the rapid rise in the value of the yen, which has made numerous Japanese products - including shoes, textiles and radios - less competitive with those of such Asian countries as Taiwan and Korea.

"We have to keep exporting our manufactured goods to survive, but we are finding our neighbors in Asia are making the goods we used to make, so we have to go into high technology in a big way," said Mitsui's Satta. "I know these days computers are delicate commondities, but our technology level must keep improving so someday there's a chance we will be able to ship lots of computers here. The Americans are good at inventing new machines, but, in the ability to apply those inventions, well, maybe the Japanese have more ability."

Opposition to the growing power of Japanese investment - estimated by top Japanese business sources at $25 billion last year, more than a third of it in the western states - is also developing in the Pacific Northwest, where highly active Japanese - owned firms are buying logs and fish in huge quantities and shipping them back to Japan for processing.

George Cassidy, president of the Partland-based Lumber Production Industrial Workers, claims Japanese reluctance to buy finished U.S. lumber instead of logs has forced the closure of more than 100 sawmills throughout the Northwest over the past decade.

"The exporting of the raw materials from which our jobs spring," Cassidy insists," is the exporting of our jobs."

George Hess, a spokesman for Weyerhaeuser, a major log exporter to Japan, says the Japanese prefer to buy logs rather than finished timber because "they are artisans. They cut their wood differently than we do." The Weyerhaeuser spokesman added that congressional legislation has forced American lumber companies to ship all their intra-national trade in American vessels and claimed that makes it far too expensive for north-western lumbermen to trade with their traditional East Coast markets.

Hess also said the rejuvenated U.S. southern timber industry and Quebec now supply most of the East's lumber needs, leaving northwestern companies to seek foreign, mostly Japanese, markets.

There is also growing concern in the Northwest about reported attempts by Japanese interests to buy out or control many Americans fishing companies in the region. Ed Furia, co-chairman of the North Pacific Ocean Protein Coalition, a U.S. fishing lobby group, said he fears that Japanese-owned companies in the Northwest are giving foreigners control of a key, important natural resource.

"I don't see anything wrong with majority investment in areas like television and cars," Furia said, "but I don't think that we should allow majority foreign investment in strategic resources."

A high-ranking executive of one Japanese majority-owned fishing firm, however, disagreed with Furia's assertion, claiming that the Japanese investors have proven a godsend for many foundering northwestern fishing companies.

"The fishing business in this country has not been all that good," said the executive, who asked that neither his name or that of his company be used. "Most of the companies which have sold out - or rather sold to - Japanese investors did so because they couldn't keep their heads above water, financially. Prices are up simply because the Japanese are willing to pay more for the fish."

Other rumblings about the Japanese power in the West are coming from Alaska, where several native American villages have had run-ins with Japanese firms seeking to purchase their abundant timber and fish resources.

"I think we're becoming very concerned about them," said Tom Richards, editor of The TRundra Times, Alaska's oldest native-owned newspaper. "The Japanese are very experienced in the corporate world, and some of our contacts with them have not been the best. The native companies are going to be very cautious in dealing with them from now on because they're trying to assume control in the fisheries area."