The current Justice Department investigation of South Korean influence buying in Washington developed from information turned over in late 1975 by Philip C. Habib, then assistant secretary for East Asia and Pacific affairs, according to sources close to the investigation.

Habib, who was U.S. ambassador to South Korea from 1971 to 1974, has recently been the subject of a campaign of anonymous letters to journalists, Carter administration officials and both Justice Department and congressional investigators charging that he encouraged and later covered up the South Korean plan to influence U.S. officials with cash and gifts.

However, in October, 1975, Habib brought directly to the attention of high-ranking Justice Department officials information about South Korean lobbying activities that was more detailed and concrete than earlier, unconfirmed intelligence reports.

At that time, the Justice Department's Foreign Agent Registration Act Section was conducting an investigation of South Korean businessman Tongsun Park had been begun the previous February after lobbyist William Timmons asked the Justice Department whether he was required to register under the act if he represented Park.

This investigation of Park had progressed to the point where Justice lawyers were prepared to seek indictments.

Habib's new information, the content of which has not been disclosed, was turned over to the new public integrity section of the Justice Department, which began the investigation that produced allegations that Park gave cash and gifts to U.S. congressmen on behalf of South Korea. The foreign agent registration case then was transferred to the public integrity section.

Sources close to the federal investigation of the South Korean influence-buying scheme say, contrary to a recent New York Times account, that they have no evidence indicating that any executive branch official withheld information or failed to take action when in possession of "solid evidence" of illegal activity by the South Koreans or U.S. officials.

However, beginning last autumn, journalists and federal officials and investigators received anonymous letters charging that Habib "had complete access to all U.S. intelligence rethem by Secretary Kissinger him-tapes of conversations in the Blue House when plans to influence key congressional figures were formulated."

According to the letters, Habib "could have used his knowledge and influence to kill these plans before they were ever put into operation" but "was restrained from (revealing them) by Secretary Kissinger himself."

The letter writes admitted they had no direct evidence that habib participated personally in planning the specific, concrete steps the South Koreans did take. Yet, through various channels including specifically detailed intelligence reporting, it is now totally proven that Habib was completely aware of every step the South Koreans were taking."

The Washington Post has found from several sources that intelligence reports between 1969 and 1974 did touch on various questionable South Korean activities.

Central Intelligence Agency operatives, for example, reportedly told Washington that Suzi Park Thomson, a secretary to then Speaker of the House Carl Albert, was a South Korean agent. Habib subsequently objected to Thomson's presence at meetings between Albert and American officials in Seoul.

The CIA station in Seoul reported to Washington that another congressional aide, Kim Kwan, who worked for both former Reps. Cornelius Gallagher (D-N.J.), and Richard T. Hanna (D-Calif.) when they were in the House, was also working as an agent in the South Korean government. William Porter, Habib's predecessor as U.S. ambassador to South Korea, reportedly objected Kim's accompanying U.S. congressmen to South Korea in 1969.

State Department officials in Seoul also complained to Washington about the intervention of Hanna and former Rep. Otto Passman (D-La.), in U.S. agency for International Development (AID) business in Seoul.

The CIA station in Seoul reported on at least five separate occasions to Washington that various congressmen had been targeted to receive cash from South Korean agents and had actually accepted it, according to information from CIA informants within the South Korean Central Intelligency Agency.

The CIA also reported to Washington on several occasions that U.S. congressmen were availing themselves of Korean offers of women, luxurious accommodations, and entertainment on visits to Seoul.

Each source contacted by the Post noted that the information available to Habib and others emanated from unusually reliable sources, including high-ranking Korean officials and electronic intercepts of South Korean cable traffic and conversations, but had no independent corroboration.

Much of the information was apparently held closely by a very small group within the CIA, State Department and National Security Council, the sources said. Much of the intelligence traffic was purposely routed around the Korean desks of the CIA and State Department, according to the sources.

State Department and CIA officials, contacted about the anonymous letters making charges against Habib believe they were written by a knowledgeable source within either the State Department or the CIA. However, all the officials contacted said they know of no substantiation for the allegations and suggest that the writer's principal motivation is probably political.