Hancho C. Kim, one of the alleged South Korean agents indicted in the congressional influence-buying scandal, has begun negotiating with House investigators to reveal what he knows about Korean bribes and gifts to U.S. officials.

If Kim agrees to talk, his testimony could be a major break for federal investigators, who have been frustrated for months in their efforts to gain firsthand knowledge of the alleged Korean payoffs.

Kim and his lawyers were seen leaving a House committee room yesterday after a 2 1/2-hour session with investigators from the House Committee on Standards of Official Conduct. Committee sources said the session involved "delicate" negotiations concerning what Kim might say and what guarantees he might get.

Peter White, the committee's deputy special counsel, and David Povich, one of Kim's lawyers, declined comment.

Kim presumably would be seeking immunity from prosecution under two pending federal indictments - one for conspiracy to bribe congressmen and lying to a grand jury, and one for income tax evasion - which were issued in September.

To gain immunity, Kim might tell about his own role, if any, in the effort to win influential American friends for South Korean. He might also have information about Tongsura Park, a businessman and socialite who has also been indicted in the Korean bribery case and who has refused to return form South Korea for U.S. trial.

Accoridng to testimony at last month's congreesional hearings on the Korean Central Intelligence Agency to buy friends in Congress and the executive branch.

The testimony indicated that Kim was the central figure in a KCIA scheme code-named "Operation White Snow." A witness said that Kim had boasted of recruiting an "advance guard," consisting of about five member of Congress, to help him make contact with a larger group of congressman.

Rep. Tennyson Guyer (R-Ohio) was a personal friend of Kim, and Kim wanted to use that connection to make contacts in the White House, according to federal investigators. Aides to former President Ford said last week that Guyer had tried to several times, unsuccessfully, to arrange a meeting between Ford and Kim.

The conspiracy indictment is a the most detailed statement to date of the charges against Kim, but it set forth few specific instances of effort to buy influence. One of the continuing mysteries in the case has been what Kim did with the $600,000 he allegedly received from Korea.

Justice Department and congressional investigators have considered Kim a likely candidate to cooperate with their probers, because he gave up Korean citizenship to settle in the United States.

Until recently, however, Kim has invoked his Fifth Amendment rights in refusing to respond to all substantive questions about the case, investigators said. Yesterday was apparently the first serious discussion about his possible cooperation. Sources said more sessions would be necessary before the two sides could reach agreement.

The probers said they badly need testimony from soemone who was directly involved in the influence-buying scheme. Much of the evidence adduced to date has been circumstantial or hearsay.

Tongsun Park, who is generally considered the central figure in the case, left the United States last fall after preliminary questioning by the Justice Department. He is now in Seoul and has apparently rejected all offers to discuss the case with American officials.

Former Rep. Richard T. Hanna (D-Calif.), a close friend of Park's who has also been indicted in the case, has spoken with House investigators without immunity.

Another potential witness, Kim Dong Jo, a former South Korean ambassador here who allegedly was personally involved in the influence-buying scheme, is now a diplomatic adviser to the South Korean president and is beyond the reach of the U.S. investigations.