South Korean businessman Tongsun Park returned to Washington yesterday for the first time in 18 months to answer questions about an alleged scheme by the South Korean government to buy influence in Congress.

Park, who is believed to be the central figure in the case, stepped off a jet at Dulles International Airport and announced: "I feel like I'm coming home." He said he plans to stay for about a month.

Park is returning to face questioning by U.S. authorities, and is expected to be grilled by the House Committee on Standards of Official Conduct. In an interview in the current issue of Newsweek, Park is quoted as saying: "I never imagined I would become such an important issue."

In a companion Newsweek interview, Kim Dong Jo, former South Korean ambassador to the United States, vigorously denied reports that he made payoffs to members of Congress.

"They are not only untrue, but also ridiculous," Kim said of the reports: "I never tried to influence American congressmen or officials by conducting such lobbying activities."

The reports were based on committee testimony by a former Korean embassy press secretary who defected. The onetime press aide said he saw Kim stuffing a briefcase with cash to deliver to some members of Congress.

Said Kim: "I have never carried a briefcase in my life, let alone stuffed it with cash. I don't know why he is telling these lies. My guess is that he is trying to justify his defection."

Park, in his interview, denied he had any connection with the Korean Central Intelligence Agency and claimed he was intimidated into making a $500,000 loan to Washington KCIA chief Gen. Yang Du Won.

The House committee investigations produced five checks totaling $500,000 signed by Park and made out to Kim Sang Keun, a former Korean embassy official who testified in committee hearings that he acted as a money courier for the KCIA.

Said Park: "Those five checks were a series of blank checks I had signed and given to Gen. Yang Du Won as a loan. . . made under intimidation. The checks were subsequently filled out to the order of Kim Sang Keun and sent to him, and he deposited them in his own account. As far as I can determine, Yang used this money for his own purposes. . . "