One by one, a panel of leading Korean businessmen let fly with their complaints that the United States is growing more protectionist and increasingly restricting their imports.

After the theme was repeated in five straight questions, Commerce Secretary Malcolm Baldrige lost his patience.

"Thank you for the same question," he began testily. "I don't know of one case where you are being kept out of the United States, but I can name 15 or 20 cases where U.S. products and services are being kept out of Korea."

The exchange, on a U.S. Chamber of Commerce videoconference between Korean industrialists in Seoul and Baldrige in Washington Thursday night, underscored the growing trade frictions between the United States and Korea.

Although the hour-long exchange began and ended with expressions of the strong strategic and economic ties between the nations, it didn't take long for the trade conflicts to emerge.

Trade between the United States and Korea, one of Washington's closest allies in the Pacific basin and one of the Asian nations that are dominating American imports, has increased greatly over the past three years and is expected to reach $15 billion for 1984. Korea is expected to sell America $9 billion worth of products while buying only $6 billion.

Korea, on the other hand, sees any perceived shutting of the American market to its products as a possible cooling of the security relationship that provides protection from communist North Korea.

"When it comes to trade issues, Korea is treated equally with other nations or unfavorably treated, even though we are your closest allies in northeast Asia," complained Jong Hyon Chey, chairman of the Sunkyong Group.

Baldrige staunchly denied that the United States is closing its markets to imports, arguing that no other nation would take America's massive trade deficit without imposing protectionist tariffs and import quotas. He also defended the large number of unfair trade cases filed by American companies as necessary to keep alive a free trade constituency in the United States.

The Koreans, who face accusations of subsidizing products for export and dumping a wide variety of goods in the United States at prices less than are charged in their domestic market, insisted, however, that complaints against them for unfair trade practices are a deterrent to their sales in America.

They also said that while Korea is becoming more free-trade-oriented by eliminating import restrictions, the United States is closing markets.

"I must object to the constant references on the part of every speaker that the United States is turning to a protectionist course," Baldrige replied. "The United States is by far the most open country in the world to imports. We have no rules as you do in South Korea keeping out mini-computers, glass and construction equipment. These all come freely into our country.

"It's hard for me to understand that we are unfairly treating you," he continued. "American companies are missing some real opportunities in Korea that I think they are entitled to."

He also challenged the Korean industrialists to open their country to American services such as advertising, insurance, accounting and banking, which face either outright bans or severe restrictions.

"We are opening the door step by step," replied Soo Chang Chung, president of the Korean Chamber of Commerce. "We would appreciate it if you would give us more time to fully study the problem and take new steps."