The federal grand jury that began investigation South Korean influence buying in Congress ended its 18 month term yesterday with the unusual step of presenting a secret report to Chief U.S. District Court Judge William B. Bryant.

The specific language of the report is not known, but sources familiar with the investigation said the grand jury wanted to make critical references to Rep. Edward J. Derwinski (R-III).Members of the grand jury were conviced, the sources said, that Derwinski was responsible for informing the South Korean government about the planned aefection of one of its intelligence agents to the United States.

Prosecutors told the grand jury that there was not enough evidence to support a criminal indictment of Derwinski. The panel then made its special report to the judge.

It could not be learned yesterday whether the report touched on other subjects. There have been indicators in recent months that the grand jury has not been satisfied totally with the prosecutors' handling of the larger influence-buying investigation.

Derwinski, who could not be reached for comment yesterday, consistently has denied that he played any role in the defection incident."I'm not the culprit in this thing," he has said.

The grand jury wanted to recommend that information about Derwinski's role in the incident be passed on to the House Committee on Standards of Official Conduct for possible disciplinary action.

The Wall Street Journal reported in October that Derwinski was the target of the leak investigation, apparently because U.S. intelligence agencies had picked up evidence of his involvement from a wire-tap or the interception of Korean embassy cable traffic.

The foreman of the grand jury handed the two page statement to Judge Bryant yesterday without commenting on its contents. The judge accepted and read the report, also without comment and said it would be sealed while he considered it.

Local and state grand juries often are charged by judges to file reports on matters they investigate. But the main duty of a federal grand jury is to vote indictments where evidence shows "probable cause" a crime was commited.

The jury, whose term ended yesterday, returned indictments against Washington businessmen Tongsun Park and Hanche C. Kim and former Rep. Richard T. Hanna (D-Calif) for their alleged roles in the South Korean government's lobbying campaign to ensure continued U.S. aid.

The unrelated leak investigation was started when Sohn Ho Young, a Korean Central Intelligence Agency agent in New York, was taken into protective custody by federal authorities just before Korean officals, apparently acting on a tip, arrived at Sohn's home.

Rep. Donald M. Fraser (D-Minn.) asked for a Justice Department inquiry because Sohn had approached his House International Organizations Subcommittee asking for asylum in the United States and the tip to the Koreans apparently came from someone close to the subcommittee.

Sources said that as recently as late last week members of the grand jury were intent on indicating one or more persons in connections with the leak investigation, but prosecutors argued against such action on the ground that there wasn't sufficient evidence.

One possibility is that some of the evidence was gatheres from highly sensitive intelligence sources, such as a wiretap or cable interest on the South Korean embassy in Washington. Prosecutors would be reluctant to introduce such evidence in court because of the chance of having to disclose those sources.

Derwinski, a 31-year-old conservative from the Chicago area, has been a longtime supporter of South Korea. He opposed the original funding of Frasers' investigation of U.S. Korean relations and criticized its direction in hearings last week.

Sohn, the KCIA agent who defected, was the star witness at the hearings, which features the the unveiling of an elaborate 1976 South Korean plan to influence U.S. officials, journalists, scholars and religiousleaders.