As protectionist pressure against Japan builds on Capitol Hill, one of the fastest growing threats to American trade in this decade has been largely ignored.

That little-noticed force is a group of newly industrialized East Asian countries -- Taiwan, Korea, Hong Kong and Singapore -- that quietly are coming into their own in Japan's back yard.

Since 1980, the U.S. trade deficit with the newly industrialized countries, or NICs, as they are known, has increased 427 percent compared with an increase of 202 percent with Japan, according to Commerce Department figures. The deficit last year with the NICs was $21.4 billion -- not quite up to the $36.8 billion with Japan, but gaining on it.

And economists say that, because those countries try to adjust their currencies to match the dollar's movements, a weakening of U.S. currency will do nothing to stem the tide of imports from them.

Generally, if the dollar declines, foreign goods become relatively more expensive here and U.S. products become relatively cheaper abroad. Thus, American exports would be expected to rise while imports would fall.

But if the NICs' currencies decline along with the dollar, they will be able to maintain their price advantage. Their exports will continue to flow into the United States, preventing any sharp improvement in the U.S. trade deficit, which is expected to reach $150 billion this year.

The NICs have been successful because they have cheap labor and are masters of copying others' technology, according to economists. Many of them say that the NICs are following in the footsteps of Japan.

"They're the Japan of the 1980s and 1990s," said Howard Rosen of the Institute for International Economics. "The point is, they're becoming Japan and we haven't dealt with Japan yet. Here we are entering the 1990s with two Japans. We really are preparing ourselves for a double whammy."

"These Asian countries are looking to the United States" for growth, "and the United States is looking at these countries, and saying 'look what you're doing to us,' " said Richard Buczynski, director of Pacific Basin Services for Wharton Econometrics.

The NICs will continue to push their exports, but they will do so very carefully to avoid protectionist pressures from the U.S. Congress like those faced by Japan, Buczynski said.

Until recently, the East Asian NICs had been largely ignored in protectionist legislation, with most of the emphasis focused on Japanese cars, electronics and telecommunications goods. However, more recent legislation has started targeting some of the NICs.

For example, a major piece of legislation would slap a 25 percent surcharge on imports from four countries with large trade surpluses if they don't buy more American-manufactured products. Those countries are Japan, Korea, Taiwan and Brazil.

Pending legislation to restrict textile imports would sharply affect Taiwan, Korea and Hong Kong.

The East Asian NICs "are growing much faster than Japan," said David Hartman, chief international economist for Data Resources Inc. The trade issue is getting "a lot of attention in Taiwan. Taiwan policy makers already are concerned about protectionism."

Exports from the NICs to the United States are predominantly manufactured goods. Most of their exports here are in electronic components, radios and televisions, telecommunications, tape recorders, toys and sporting goods, computer parts, calculators, clothing and textiles.

In 1983, the NICs supplied 60.9 percent of U.S. imports of clothing, 27.3 percent of U.S. imports of electric machinery and 52.8 percent of footwear. Following Japan and the European Community, the NICs were the third-largest contributors to the growth of the U.S. trade deficit last year, which reached a record $123.3 billion, economists said.

Economists said they expect the NICs in varying degrees to devalue their currencies if the dollar declines. In Korea, devaluation may be somewhat difficult because the currency's value is closely linked with political success. If the currency loses value, the government in power is assumed to be doing something wrong, Buczynski said.

Taiwan, which has the largest trade surplus with the United States, is very conscious of protectionist sentiment in the United States. It would be wary of reducing its currency's value faster than the dollar's decline for fear that it would encourage too many exports to the United States that would be countered by legislated quotas or tariffs against its goods, Buczynski said.

Hong Kong's currency is pegged to the dollar. If the dollar falls, it gains no advantage in the U.S. market but prices of its goods will fall relative to those in other countries, Buczynski said. Thus, Hong Kong may increase its exports to Europe, for example, Buczynski said.

Singapore's currency also floats, similar to Korea's, and it is expected to be adjusted downward when the dollar falls, but not by as much as the dollar, Buczynski said.

Between 1980 and 1984, the U.S. trade balance with Singapore moved into deficit for the first time and the deficits with the three other NICs deteriorated sharply, economists said. Because these countries can diversify easily into new products, economists expect them to grow in importance and to compete directly with the United States in capital-intensive and high-technology goods.

In the last couple of years, as the dollar has gained strength, the NICs' currencies also appreciated, making it difficult for them to sell to other countries because their goods became relatively more expensive. This inability to break into other markets has made it even more imperative that they ship goods to the United States, economists said.

Between 1982 and 1984, exports to the United States from Hong Kong increased 55 percent, from Taiwan 71 percent, from Korea 68 percent and from Singapore 85 percent, Hartman said.

"They started in the early 1980s, mostly with consumer goods, toys, clothing," Hartman said. Korea and Hong Kong particularly moved into the high-tech areas, he said.

Additionally, American and Japanese companies are manufacturing goods in the NICs for export to third countries.

Growth in the European Community has outpaced the NICs over the last four years, Rosen said. But those gains have been due largely to changes in the value of the dollar and not because of any growing, long-term competitive edge.

"With Europe, it's all exchange rate," Rosen said. "That's all temporary. They're not competitive."

In 1980, the United States had a $15.7 billion trade surplus with Europe that was whittled down to a deficit of $13.3 billion last year. During the same time, the trade deficit with Japan grew from $12.2 billion to $36.8 billion, and that with the East Asian NICs grew from $4.1 billion to $21.4 billion, according to Commerce Department figures.

To determine the path of the NICs, Rosen suggested Japan as an example. "So far, they've shown themselves to be good copiers," Rosen said of the NICs.

"The goods they are selling in the United States are even cheaper when compared to the goods Japan shipped here in the 1960s," he said.

"The best thing to do is look at Japan," Rosen said. "They followed the same path of starting with textiles, steel, more of the copying type of products, video display terminals, televisions, transistors, all of this stuff Japan was in."

"If you want to see what Korea will be like, look at Japan," Rosen said.

However, unlike Japan, if the U.S. economy slides into recession, the NICs' domestic growth would suffer, economists said.

According to Data Resources Inc., Taiwan "would experience the most significant decline in growth of any nation in the world" if the United States had a recession. Its growth would decline from 7 percent this year to 3.1 percent in 1986, DRI said.

"Korea shows a very similar pattern of response since its dependence on the U.S. market is only slightly less than Taiwan's," DRI said. "With the most open economy of any nation its size, Singapore would see its gross domestic product growth fall from 4.7 percent to 1.3 percent if the U.S. moved into a recession next year. Despite a quick and sharp rebound in trade in line with the U.S. recovery, Singapore's domestic economy would be sufficiently weakened by the episode that fixed investment would not recover by 1987.