The most vocal opponent of a sweeping House international relations subcommittee study of U. S. - South Korean relations is now urging that House budget overseers cut the investigation's funding.

Rep. Edward J. Derwinski (R-Ill.), who lost an earlier attempt to prevent the inquiry, is circulating a letter to ranking members of the House Administration Committee calling the proposed study "a redundant inquiry that will inevitably mimic" other investigations of the South Korean goveernment's lobbying efforts in the U. S.

Derwinski said yesterday that he would be satisfied if the House Administration subcommittee on accounts cuts the proposed staff budget in half when it meets to consider the $356,700 request on Wednesday.

Rep. Donald Fraser, chairman of the investigating subcommittee, said yesterday that he was "surprised and disappointed" to learn late last week that Derwinski, ranking minority member of his cubcommittee, had written the Feb. 10 letter without informing him.

"I also understand that they made some effort to make sure we didn't know about that letter," Fraser said.

he House International Relations Committee voted 19 to 4 last month, over Derwinski's objections, to direct Fraser's international organizations subcommittee to undertake the investigation.

It was unclear yesterday whether Derwinski's latest attempt to stop Fraser's investigation was having any effect. But Toni Grant, staff director of the accounts subcommittee, said there did seem to be "mounting opposition" to the Fraser inquiry.

She noted that the subcommittee already had recommended full funding for a $530,000 ethics committee investigation of reports House members accepted cash and gifts from South Korean agents.

Rep. John II. Dent (D-Pa.), the accounts subcommittee chairman, has been looking closely at all committee budgets in an attempt to cut costs, Grant said. "The justification we've seen so far has been rather sparse," she said of the Fraser budget proposal.

Derwinski said yesterday that the intended 18-month study of U.S.-South Korean relations isn't warranted "because I don't think the Korean style of diplomacy is all that different from other countries . . . The Koreans have been rather ham-handed about it, evidently. But we have enough other issues to worry about."

He said Fraser's description of the several years ago of the South Korean things we've already seen in the press or heard in his earlier hearings."

Fraser counters that his subcommittee's investigation is needed to examine policy questions that go beyond charges of misconduct by individual members of Congress.

He plans to focus considerable attention on the actions of executive branch agencies who apparently knew several years ago of the South Korean plan to buy influence on Capitol Hill, he said.

In addition, Fraser said he wants to examine further:

. Ties between the South Korean government and the Unification Church of evangelist Sun Myung Moon.

. Extortion of political funds from American companies by the regime of President Park Chung Hee.

. Influence buying in the U. S. academic world and the media by South Koreans.

. Harassment by the KCIA of Korean-Americans.