They are not the sort of results that usually confront the technocrats who manage the perpetual-motion economy in South Korea: exports down, investment down, overall economic expansion down.

To their dismay, these numbers have been appearing month after month in the ledgers in Seoul this year, symptoms of South Korea's most serious stumble since 1980 in its two-decade-old race toward industrialization.

Stagnation in varying degrees also is washing over the other three of the so-called NICs, the high-growth, "newly industrialized countries" of East Asia -- Taiwan, Hong Kong and Singapore. In each of these export-oriented economies, a slowdown in purchases by the affluent countries, particularly the United States, plays a role.

The experience has given Korean planners added appreciation of the fragility of their entire development strategy, which has run up the world's fourth-largest foreign debt, about $45 billion.

The past months' events also have brought new concern -- and some anger -- over legislation before Congress that would take another big slice from South Korea's exports. The aim in Washington is to cut imports and reduce the U.S. trade deficit with South Korea, which reached about $2.5 billion in the first nine months of this year.

South Koreans say their government is trying to cut the deficit on its own. "The U.S. administration should be careful not to push someone who is doing his best," said Dr. Koo Bohn Young, senior counselor to the deputy prime minister.

In one of the most sustained economic expansions in modern history, South Korea, under a succession of authoritarian, military-dominated governments has boosted gross national product per person, a broadbrush measure of wealth, from a rock-bottom $87 in 1962 to today's level of about $2,000.

Growth halted suddenly in 1980 -- GNP actually contracted by 5 percent -- due to the second oil shock and political turmoil that followed the assassination of President Park Chung Hee. But it resumed in subsequent years.

Today's trouble is small compared with those in 1980, and in many countries would not be considered trouble at all. Real economic expansion has been nose-diving since it registered almost 13 percent in the first quarter of 1984. By the second quarter of this year, it was down to 2.7 percent, but it was growth nonetheless.

Figures for 1985 through July show exports contracted by about 3.5 percent from that period in the previous year. Most analysts blame most of the growth slowdown on these figures. This economy depends on exports for about 35 percent of GNP, with the United States as the largest market.

"If the United States drags, you can figure in two months you're going to see the Korean economy drop," said Samuel A. Clark, general manager of the Seoul branch of Security Pacific National Bank.

Growth in the United States has dropped from 10 percent to 2 percent. That has hit a wide range of products in which the Koreans specialize. In the first seven months of 1985, exports of electronics were down by 5 percent, shoes by 2 percent, ships by 24 perecent, light industrial goods by 5 percent.

In addition, new construction deals in the Middle East, a multibillion-dollar business for Korean-based companies, continue to fall off as the low price of oil leaves many countries there strapped for cash. Payments on old deals also are delayed.

Investment at home fell off, too, as people with money lost a bit of their usual robust confidence in the economy, which has evolved into a $81-billion-a-year operation.

President Chun Doo Hwan has relied on growth to build his country's image in the world's eye and his own among South Korea's 40 million people. Lately, however, his government has had the uncomfortable feeling of being on the defensive.

The public, newspapers writers and politicians have become more aware of the enormity of their country's debt and have spoken out. The fact that most of it is owed to foreigners strikes a raw nerve among nationalists.

The government has responded with a collection of pump-priming efforts. It has devalued the local currency, the won, against the dollar to stimulate exports. It has begun moving on tax and budget measures to prop up the construction industry and create jobs.

It also has applied some austerity measures to rein growth of foreign debt, which continues to creep upward despite the slowdown.

But many Koreans, in fact, are more concerned about the size of the debt than are the banks it is owed to. "Confidence is still quite strong," said Arjun K. Mathrani, general manager at the Chase Manhattan branch here. New loans continue to flow in, on terms that would make the big debtors of Latin America envious.

South Korea still has more than enough money to service its debt (monthly payments come to about $560 million). Imports have fallen as well as exports, meaning balance-of-payments figures are about the same. "Our debt-service profile will not change much from our original estimate," predicted government counselor Koo.

Bankers continue to feel that funds lent here generally go to productive use.

Though the political scene continues to simmer, with small groups of students battling police on the campuses and opposition politicians pushing hard in the National Assembly, bankers do not see it as any significant threat to the national credit rating.

Korean officials maintain that the slump has bottomed out. But some foreign analysts are not so sure, pointing to continuing problems in foreign markets.

Perhaps of more concern to planners here are Congress' protectionist bills. They also are watching for effects of President Reagan's recent decision to seek to open the Korean life insurance market to U.S. companies.

South Korea argues that, unlike its neighbor Japan, its overall payments are in deficit and its surplus with the United States is tiny compared with Japan's.

There is a recurrent feeling that Korea is to be punished for Japan's transgressions, or, perhaps worse, for its own success.

Seoul's eyes right now are on the textile bill, which officials here say would cut Korea's $2.6 billion in exports to the United States in that sector by about 30 percent. (However, other accounts say much of the loss could be made up quickly by switching to product lines not covered by the bill.)

"My government is considering some sort of retaliation if that bill passes," said Jin Kim of the Ministry of Industry. He would not elaborate, but suggested it would be constraints on specific items imported from the United States.