"The Koreans," said an American official a few months ago,"have an infinite capacity for absorbing reassurance."

He was commenting on South Korean fears that the gradual with-drawal of U.S. troops meant that the American back was being turned on this Asian ally.

His observation is doubly accurate today because South Korea has a new and very bad case of the jitters. Some of its leaders suspect that the United States may be trying to make a deal for a peace settlement with the Communist north and any hint of that starts the tremors rolling.

Their fears are reinforced by recent Asian history which, as they read it, does not offer grounds for optimism.

Item: It was disclosed this week that an American table tennis team will play in an international tournament next year in the North Korean capital, Pyongyang.

The South Koreans recalled that it was Ping-Pong that launched the friendly relations between China and the United States, much to the consternation of another old American ally, Taiwan.

Item: It has been rumored for weeks that the United States is considering a plan to arrange three-party talks with North and South Korea to map a peaceful settlement of their 30-year-old conflict.

The Koreans also recalled how the United States once dragged another American ally, South Vietnam, to the peace talks in Paris.

In both cases, U.S. officials quickly gave the South Koreans the expected reassurances but the jitters only got worse. Table tennis is a private game, they said, and Americans can go to Pyongyang when invited. But, asked the South Koreans, why didn't you inform us last August when your State Department first learned of the match?

The three-party peace talks, expleined the U.S. officials, is only an idea that should be considered and should not be rejected out ot hand. By the time that advice was digested by the South Korean government and passed on to the press, it had been transformed into an American pressure play to force acceptance of the idea.

The current jitters follow a series of events that have combined to provoke rare signs of anti-Americanism in South Korea. It began with the troop withdrawal annoucement, continued through the humiliating Tongsun Park affair, and came to a head in the reaction to the alleged bugging of President Park Chung Hee's official mansion, the Blue House.

A number of interviews last week failed to uncover a single South Korean politician or government leader who believed the U.S. denial of the bugging report.

All of these events combined to produce a new bitterness and a lot of complaints about big powers who push small friends around. Until recently, President Park made sure this unhappiness was contained. But the protests at the U.S. Embassy and the rush of press criticism showed that he is ready to let the resentment show.

Even before the bugging incident blew up, the Park government's intellectual supporters were up in arms. Borrowing a line from former senator William Fulbright, Kim Jun Yop, the director of Korea University's Asiatic Research Center, accused the United States of indulging in a new "arrogance of power."

Kim referred to a congressional report that references to secret meetings in the Blue House had appeared in American intelligence reports - a violation of law more serious than anything Tongsun Park did, he said.

"There seems to be a presumption that it is all right for the powerful to violate the laws by which the weak live, while the weak should not go unpunished for daring to break the laws commanded by the powerful," Kim wrote.

For Koreans, these slights and injuries to pride have an unpleasant irony because they occur at a time when their country is being told to become more independent and self-reliant.

Yet, the government has been forced to turn Tongsun Park over for questioning and pressed to make a former ambassador, Kim Dong Jo, available for some form of testimony in the bribing scandal. Then came the allegations that "big brother" had been bugging the presidential mansion.

All were examples of South Korea's client-state status. Even the recent announcement that the United States is delaying its troop withdrawal reminded some Koreans that Washington is still in charge. "It was an American decision," said one official. "We could have nothing to do with it."

The South Koreans are convinced that North Korean leader Kim II Sung is attempting to exploit such divisions and animosities. The peace-talk flurries emanating from Yugoslav President Tito, who suggested the three-party talks, and Romanian President Nicolae Ceausescu reflect the North's feeling that it can now drive a wedge between South Korea and the United States, they assert.

And the merest hint of that makes the South Korean jitters all the worse and the traditional American reassurances do not work much anymore.