SEOUL -- South Korea, an economic basket case two decades ago, has stunned the world by quickly moving into the ranks of industrially developed countries, poised to become a "second Japan." Despite global economic uncertainty, South Korea chalked up sizzling growth rates of about 12 percent for 1986 and 1987.

Now, faced with the threat of protectionism and recession in its major export markets, South Korea might seem to be heading for a bad year in 1988. Not at all.

The leader of Asia's four-country pack of "economic tigers" is officially forecasting an 8 percent jump in 1988 gross national product, which measures the value of goods and services produced. As before, the growth will be fueled by aggressive exports, particularly to the United States. And that upbeat GNP forecast may be too low, according to some economic experts.

"I'm not sure how much weight you can put on {government} forecasts because they're generally conservative," said Thomas Brown, president of the American Chamber of Commerce in Seoul. "It seems like every year the Economic Planning Board and the Bank of Korea come out and predict 8 percent growth, but the real figure hits double digits."

A new element in the growth equation will be far greater government spending on "basic structure" items, such as public housing and better roads. President-elect Roh Tae Woo made a series of pledges during last year's election campaign to improve living conditions for average Koreans, and he will be under considerable pressure to deliver on those promises.

"I think this is a very important turning point for Korea's economic strategy," said Kwack Tae Won, a director of the state-run Korea Development Institute. "Our society is changing and the international economy is changing."

By many measures 1988 should be the year in which South Korea's economy cools down considerably. Externally, it faces protectionism exacerbated by slow growth in Western economies. On the domestic front, wages are rising and strikes may reoccur in the spring when contracts are renegotiated by fledgling unions.

The Reagan administration is also pressuring the South Korean government to rapidly appreciate the country's currency, the won. Officials are reluctant to do so because a stronger won could reduce American purchases of Korean products by making them more expensive. An official at the Economic Planning Board here contends that every 1 percent increase in the won's value against the dollar causes a 2 percent drop in South Korean sales in the United States.

On top of all that, the United States and the Common Market are threatening trade sanctions if South Korea fails to open its relatively closed domestic market. Some cynics suggest that Japan looks like a free-trade zone compared to South Korea, where upwards of 95 percent of the cars on the road are locally made, thanks to prohibitive tariffs on foreign auto imports, and where restaurants serve only South Korean beef due to a ban on meat imports. Foreigners are prohibited from direct investment in Seoul's burgeoning stock market.

Despite the potential problems, many experts attribute Korea's continuing bullish growth prospects to such underlying strengths as a relatively low-paid yet highly educated and motivated work force. When strikes spread through the country last August and September, many people warned of the beginning of the end of the country's economic miracle. But the result has been far from cataclysmic. Although the strikes temporarily hobbled production, output soared to record levels once factories reopened.

However, the wage hikes and the specter of further strikes may hasten an ongoing transformation to capital-intensive industries from labor-intensive industries, the building blocks of South Korea's economic success. With China, the Philippines and Indonesia benefiting from even lower-paid work forces, South Korea has been gradually losing its competitive edge in such labor-intensive industries as textiles. "The people in Korea who were making their money solely on the back of cheap labor will be hard hit," warned Scott Kalb, the director of the Seoul office of the London brokerage James Capel & Co.

But with the move to high-tech industries going well, the winners should far outnumber the losers in South Korea, analysts say. The country's conglomerates -- such as Hyundai, Samsung, Lucky-Goldstar and Daewoo -- are increasingly focusing their activities, and betting their futures, on higher-priced electronic and industrial products, slimming down their reliance on such traditional strong points as construction or shipbuilding.

"We are gradually changing from heavy industries to sophisticated industries," says Chung Se Yung, chairman of the Hyundai Group. Hyundai, forecasting an 18 percent sales jump in 1988 to 20.1 trillion won ($25.4 billion), reportedly plans to pour 1 trillion won into plant modernization and expansion, while setting aside 350 billion won for research and development projects.

Many economic experts believe the gamble will pay off. They point to the fact that South Korean workers, while relatively well-paid by Third World standards, receive far lower wages and work longer hours than laborers in Japan and the United States. And the quality of their high-tech products, while still inferior to Japanese or American goods, is rising quickly, experts believe.

They say the record-setting success of Hyundai's Excel car is a sign of South Korea's ability to compete in sophisticated product areas against Japan and the United States, rather than against China and the Philippines in low-tech sectors.

On top of this, South Korea could fare quite well in an era of penny-pinching consumerism. Because of the higher costs for many Japanese and American goods, price-conscious consumers in the United States might opt for cheaper South Korean cars or VCRs rather than expensive Japanese or American models.

"The Koreans can do okay in a stagnant market," said a Western diplomat who closely follows economic affairs. "Their share can expand even if the market doesn't." For the most part, increased Korean sales in the United States will probably come at the expense of Japanese sales, experts say.

A big question, though, is whether South Korea will retain the broad access it had in 1987 to American and West European markets. Because of Seoul's slowness in opening its own markets, Washington and the Common Market are threatening to impose trade sanctions.

In addition, the United States has removed South Korea and the three other "economic tigers" from the list of developing countries eligible for preferential tariff treatment, effective next January. The Common Market also has lifted a set of special trade tariffs previously accorded to South Korea.

"There will be increased tension in trade relations because the volume of trade between the two countries exceeded $25 billion in 1987," said Kim Chul Su, a deputy minister in the Ministry for Trade and Industry. "With that kind of trade volume, there are bound to be trade problems. I am hopeful that we'll be able to solve these problems through dialogue."

Washington, which is quickly abandoning the low profile it adopted during South Korea's volatile presidential election campaign, is already embroiled in a dispute over Seoul's restrictions on imports of foreign beef and cigarettes.

Roh's campaign pledges to protect domestic farmers will make it difficult for Seoul to offer substantial concessions in the near term. And even if the current dispute is amicably settled, there are many other sore points that will be the source of greater irritation in the coming year, officials warn.

"In the past, trade friction was marginal," said Kenneth Park, an executive vice president in the international division of the Samsung Group. "Now it's our main problem."