A spasm of fear is running through major allies of the United States that escalating demands on South Korea by famed investigator Leon Jaworski threaten to undermine established diplomatic practice and jeopardize their own relationship with the United States.

By using threats to force a former South Korean ambassador to testify in the House ethics committee's Korean scandal probe, Jaworski has alarmed not only foreign allies but leaders of the House as well. His threat: If the testimony is withheld, he will insist that the House vote to shut off U.S. aid to Korea. But under the Vienna Convention, approved by the Senate in 1965, no foreign diplomat can be compelled to give evidence.

Former Ambassador Don Jo Kim, now an aide to President Chung Hee Park in Seoul's Blue House, is wanted by Jaworski as a material witness to the alleged bribery of U.S. congressmen. Israel, Iran, Saudi Arabia and other large-scale recipients of American aid have quietly informed congressional leaders that they, too, would feel threatened if Kim submits to Jaworski's threats.

A similar Jaworksi threat against the U.S.-South Korean military alliance is partially responsible for Persuading the Seoul government to order Tongson Park to testify fully and freely before the ethics committee. Actually, the deal that is bringing the money-dropping Park back here next week was mainly stitched together by the Justice and State departments.

The Vienna Convention, now reinforced with quiet but rising pressures on Washington by U.S. allies to observe it scrupulously, bars the United States from even approaching the Korean government with a similar deal for Dong Jo Kim. U.S. Ambassador Richard Sneider was ordered back to Washington last weekend for talks about the possibility of "persuading" the Koreans to let him submit a statement. However, pressure is out of the question.

The present Korean ambassador, Yong Sik Kim, told House Speaker Thomas P. O'Neill Jan. 31 there could be no chance whatever for the United States to coerce Seoul into compelling Dong Jo Kim to testify. When O'Neill asked whether that ruled out a "dialogue" - presumably long distance - the ambassador said nothing that violated the Vienna Convention would be possible.

That leaves the ball in the court of the hard-driving Jaworski, Watergate hero turned Korean-scandal prober. Even House leaders privately are fearful of military and foreign-policy implications of congressional reprisals against South Korea for refusing to produce Dong Jo Kim. What, then, is then source of Jorski's power to carry out his threat of reprisals?

The answer is partly his towering reputation as the nations's preeminent prosecutor of official scandal. Beyond that, however, it rests on Jaworski's flat statement on "Meet The press" Feb. 5 that "there are a few" present members of Congress who could be charges with "crminal misconduct" in the Korean scandals. Justice Department probers definitely have not yet reached that conclusion, and never reach it.

But having labeled "a few" sitting members as likely to be found guilty of bribery ot prejury, Jaworski has covered the whole Congress with deep suspicion. "Jaworski's threat of congressional retaliation against South Korea)$ is a most drastic one in the case of Dong Jo Kim," a leading Democrat on the House International Relations Committee told us. "But we are so sensitive to the integrity problem that be could deliver on it."

One House Republicaan leader privately admits the true reason Congress would risk alienating its allies and gravely damaging its vital defense agreement with Korea: "It's not total cowardice but it is a little bit craven. Given the low esteem of Congress, it's the equivalent of Richard Nixon saying, "I am not a crook,' and not daring to tell Jaworski that he's going too far to prove it."

This Republican leader - never remotely touched by any aspect of the Korean scandal - would definitely vote to cut aid to South Korea if Kaworski presses his case that far. Careful Whit House and State Department head-counters see no chance at all of defeating Jawworski if such a vote were held today.

There can be little doubt that Jaworski will make good on his threat if South Korea protects its diplomatic rights under the Vienna Convention. He tells any congressman who asks that failure to get testimony from Dong Jo Kim will compel Jaworski to inform the American voters his investigation cannot succeed.

Such madcap investory antics may further endhrine Leon Jaworski in the hearts of his countrymen. But the cost to American interesrts throughtout the world could be exorbitant.