The Justice Department's investigation of South Korean influence-buying in Congress could produce another half-dozen indictments of former or present members if truthful testimony could be obtained from accused agent Tongsun Park.

Without that testimony the single current case against a former member is likely to be the last.

That's the Justice Department's current assessment of its two-year inquiry. And it explains why three department officials flew to Seoul two weeks ago in an all-out but unsuccessful effort to arrange for questioning Park.

One Korean government official has told The Washington Post that "under no circumstances" would the Seoul regime let Park leave the country. "The man is a bomb," he said.

The official explained that his government felt Park was capable of saying anything "in his own interest." And if Park felt it was in his interest to implicate his government, he wouldn't hesitate to do so "for his own selfish purposes," the official added.

Korean officials have claimed they tried to convince Park to return to face a 36-count U.S. felony indictment charging that he took part in a Seoul-sponsored campaign to bribe members of Congress.

But it seems clear that the Korean government was concerned more about the damage it might suffer from Park's testimony than about the adverse political fallout from its non-cooperation.

Congressional support for continued military aid to Korea has eroded so much since the failure of the Justice Department talks in Seoul that House leaders have decided to postpone hearings on a new $800 million aid package.

Park's testimony is considered the crucial and missing link in several possible criminal cases because in many instances he is believed to have made cash payments directly to members of Congress with no other witnesses present.

In the case of former Rep. Richard T. Hanna (D-Calif.), the only member of Congress indicted in the investigation so far, there is evidence that he received payments from Park by checks, which are easily verifiable.

Benjamin R. Civiletti, head of the department's Criminal Division, said in a recent interview that he made clear on his visit to Seoul that Park's testimony was "critical to the completion of our investigation."

Without that testimony, he said, the Justice investigation was 95 per cent finished, and future indictments were in doubt unless there was a break.

The federal investigators are known to be hoping to convince both Hanna and Hancho C. Kim, a Korean-born naturalized U.S. citizen and Washington-area businessman also indicted, to provide them with evidence on others who took cash or gifts.

Hanna has been charged with joining Park in convincing the Korean Central Intelligence Agency to provide funds for the scheme and with passing some of the money to other members of Congress.

Kim is alleged to have received $600,000 in cash from the KCIA from his part in the same lobbying effort. Both Kim and Hanna have denied the charges.

The Justice Department's investigation has been hampered by other missing witnesses. For instance, because of diplomatic immunity problems, investigators have not even attempted to question former Korean Ambassador Kim Dong Jo, who was described before the House Committee on Standards of Official Conduct last week as having made cash payments to at least one House member.

Investigators for that parallel but separate inquiry are known to want to question Kim, who is now a top Blue House Adviser to Korean President Park Chung Hee, and other former diplomats.

Loen Jaworski, special counsel to the House inquiry, said he refused an invitation to Seoul to question only Tongsun Park.