The federal investigation of South Korean influence-buying here has been broadened by allegations to the FBI that the Korean Central Intelligence Agency gave $600,000 in cash to a local Korean-American businessman to distribute to U.S. congressmen.

FBI agents have been told by Kim Sang Keun, the KCIA official who agreed last November to cooperate with the FBI, that he gave the cash in 1975 and 1976 on instructions from Seoul to Hancho C. Kim, a Korean-born Washington businessman who is also a trustee of the American University.

Sources close to the federal investigation said that, according to Kim Sang Keun's account, Hancho Kim was supposed to pass the money in large amounts to several congressmen not previously suspected of being targets of South Korean bribes. The names of these congressmen could not had provided names to federal investigators.

In an appearance before a federal grand injury and an interview last October with The Washington Post, Hancho Kim denied any wrongdoing and said he had nothing to do with South Korean influence-buying here. He also specifically denied allegations about the $600,000 in an interview published in The Washington Star yesterday. But in response to new inquiries from The Post this week, Hancho Kim's lawyer instructed him to refuse further comment.

At the time of the alleged cash transactions, according to the sources, the KCIA was trying to establish a second conduit for money and gifts to U. S. officials, paralleling that allegedly provided by globe-trotting South Korean businessman Tongman Park.

Hancho Kim spent 45 minutes before a federal grand injury here last October answering questions about his friendships and social contacts with various KCIA agents working out of the South Korean embassy here.

At that time, federal prosecutors were apparently basing their questions on information from sensitive intelligance reports that Hancho Kim was to contact several U.S. congressmen. Hancho Kim denied the allegations.

Earlier in 1976, the FBI conducted surveillances of Kim Sang Keun's late night visit to Hancho Kim's home in Lanham, Md. The visits were considered suspicious, according to sources, because Kim Sang Keun, then working for the KCIA, parked his car some distance away and walked through suburban side streets to Hancho Kim's house.

In an October, 1976, Washington Post story, Hancho Kim was quoted as saying that Kim San Keun had been coming to his home to pick up cosmetics and lingerie that Hancho Kim's wife bought for the wife of Yank Doo Won, then the third-ranking KCIA official in Seoul. Hancho Kim said he understood that Kim Sang Keun arranged for items to be sent back to Seoul by diplomatic pouch.

In mid-November, 1976, Yang Doo Won, known as Lee Sang Ho while serving in the South Korean embassy here from 1972 to 1973, was mysteriously fired by the South Korean government. South Korean sources said at the time that Yang was dismissed for missing diplomatic pouches for shipment of cosmetics back to Seoul.

By late November, Kim Sang Keun, face with orders to return to Seoul himself and possibly be disgraced for press accounts of his use of diplomatic pouches and his meetings with Hancho Kim, sought FBI protection here in return for his cooperation in the investigation of alleged bribery of U.S. officials.

In mid-December, according to sources, Kim Sang Keun apparently told federal investigators that Hancho Kim had been recruited as a South Korean agent during a 1975 meeting with South Korean President park Chung Hee in Seoul.

According to sources, Kim Sang Keun said he received from Seoul in diplomatic pouches in 1975 and 1976 the $600,000 in cash, which he passed on to Hancho Kim for distribution in several specified large gifts to certain U.S. congressmen.

Last October, while federal investigators were examining his financial records, Hancho Kim acknowledged to The Washington Post that he had received large quantities of cash from Korea during 1975 and 1976. But he said he received the money as a family loan from his brother-in-law. He said the loan was to provide operating capital to offset losses in his cosmetics business, the John and Bee Dee Co.

Internal Revenue Service investigators are re-examing Kim's records now, according to sources close to the investigation.

In January, after traveling to Seoul and back, Hancho Kim retained the firm of Williams, Connolly and Califano to represent him. Previously, Kim had been represented by teo other local law firms. Vincent Fuller, Kim had been represented by two has declined to discuss the case.

Hancho Kim came to the United States in 1954 to attend Findlay College in Findlay, Ohio, and became a U.S. citizen. He stayed out of Korean politics until 1973 when he made the first of several trips to South Korea, he said.

He wrote signed articles that appeared on The New York Times Op-Ed page in January, 1975, and in The Washington Star in September, 1976, defending the Park Chung Hee regime.

Kim also tried unsuccessfully during 1975 to hire Victor Gold, former press secretary to Cive President Spiro T. Agnew.

Gold told The Washington Post last October that Kim approached him for both his writing talents and his contacts in the media here and in New York. Gold said he made some appointments for Kim with a friend at CBS.

Kim also briefly retained public relations man Julian Scheer to open doors for him at The New York Times Scheer said he dropped Kim as a client because Kim offended a Times editor by offering to pay for a Times reporter's trip to Seoul for an exclusive interview with President Park Chung Hee. Scheer said he billed Kim, but has never paid.

In January, 1976, Hancho Kim hosted a dinner for Dr. Park Chung-Soo, a university professor in South Korea who founded the Korean Research Institute, which was recently linked to questionable commission payments made by an American corporation to South Korean agents to do business in South Korea.

The dinner for Dr. Park was also attended by South Korean Ambassador Hahm Pyong-choon, KCIA station chief Kim Yung-Hwan, and Col. Lee Kyoo-Hwan, a military attache with connections to the Korean Research Institute.

Dr. Park also was here last October, according to sources in the Korean community, to try to establish informal contact with members of the Carter campaign staff on behalf of the South Korean government. Carter campaign officials have told The Washington Post they have no record of any conttact with Dr. Park.

Sources close to the investigation said they have received no allegations indicating that any of the candidates in the 1976 U.S. presidential primaries or general election were approached with either cash or campaign contributions.