A former State Department specialist on Korean affairs said yesterday that South Korean agents made cash payments to Japanese politicians in order to promote a favorable climate in Tokyo for the Seoul government's political interests.

Donald L. Ranard, head of the Department's Office of Korean Affairs from 1970 to 1974, said in an interview that the Korean payoffs went to members of Japan's ruling Liberal Democratic Party.

"There is absolutely no doubt in my mind about this," said Ranard. "CIA reports out of Seoul and Tokyo said that the Koreans were involved in payoffs to Japanese politicians."

Allegations of widespread influence-purchasing activities by Korean agents in the United States are the target of investigations by a House committee and the Justice Department.

According to reports, the Koreans spent between $500,000 and $1 million a year earlier this decade in cash, gifts and campaign contributions to U.S. congressmen and other officials to insure favorable treatment for South Korea in Washington.

Senate Minority Leader Howard H. Baker (R-Tenn.) said Sunday that as many as 50 members of Congress may be involved in the scandal.

Ranard retired from the Foreign Service in 1974 and is now director of the Center for International Policy, a private group that dissenimates information about U.S. relations with Third World nations. One of the center's objectives is the promotion of human rights abroad.

Ranard said the chief purpose of the alleged payoffs was exchanged hands. He said the payoffs took place during the four-year-period he was head of the Office of Korean Affairs.