The Central Intelligence Agency acknowledged yesterday that at least one of its officials considered liquidating a high-ranking Russian KGB defector who had offered to testify about Lee Harvey Oswald's activities in the Soviet Union.

The CIA officials in charge of the defector, Yuri Ivanovich Nosenko, were so preoccupied with breaking him down and making him confess he was a liar that they paid little attention to what he had to say about the Oswald case or anything else.

New details about Nosenko, regarded by some as one of the most important Russian defectors to this country and by others as a Soviet double agent, began to emerge yesterday before the House Assassinations Committee.

CIA spokesman John L. Hart, who was called out of retirement because of his expertise, called the agency's handling of the Nosenko case "an abomination."

Nosenko, who claimed to have supervised Oswald's KGB (Soviet secret police) files in the Soviet Union, defected on Jan. 20, 1964, weeks after the assassination of President Kennedy.

But, according to Hart, the mishandling of the Nosenko case had already been set in motion. Several years earlier, when Nosenko first contacted the United States about defecting, the CIA counterintelligence staff headed by James J. Angleton concluded from afar that the Russian could not be trusted.

Instead, Hart reported, they took the word of an earlier Soviet defector, a man identified to the House committee as "Mr. X." who "was jealous of other defectors."

Actually, Hart disclosed, Mr. X, a KGB official who had defected in 1961, had been "diagnosed by a psychiatrist, and separately by a clinical psychologist, as a paranoid."

The CIA ineptitude, the committee was told, began with the very first contacts Nosenko made with the agency in June 1962 in Geneva where the KGB had sent him to keep an eye on the Russian delegates to a disarmament conference. Free to roam the city, he identified himself to the CIA and offered information for 900 Swiss francs, according to a House Assassinations Committee staff report that was made public.

"He explained he needed the money to replace KGB funds he had spent on a drinking spree," the report stated.

Hart, who reviewed the Nosenko case for the agency on special assignment in 1976, picked up the story from there. The KGB in Moscow still regarded Nosenko as loyal when they sent him to Geneva in 1962, Hart said, but he was so nervous about being watched by KGB officers that he went to extraordinary lengths to make sure he wasn't followed.

This consisted of visting four of five bars, having a scotch and soda in each, before each clandestine meeting in a CIA secret "safe house." There, Hart said, CIA officials plied him with more liquor and "he continued to drink throughout the interrogations."

Hart said Nosenko, now rehabilitated and living in the Washington area under a new identity, told him only last week: "'I must tell you honestly at all of those meetings, I was snookered.'

"You mean you were drunk?" Hart said he responded.

"'Yes, John, I was drunk,'" Hart quoted Nosenko as responding. As a result, Hart said, "in some cases he exaggerated the importance of his activities. In other cases he didn't know what he was doing. He was simply talking."

The mistakes, Hart recounted, were compounded by the two CIA officials sent from Langley headquarters to interview Nosenko; one who took the notes, as though they were verbatim transcripts, was not fluent in Russian. Tape recordings were made, but they were not transcribed. As a result, when Nosenko said he went to the Frunze Naval Prepatory School, the notes had him going to the more famous Frunze Military Academy.

"He never said this," Hart explained, but later the fact that he never went there was held against him.

The CIA spokesman said the intelligence Nosenko produced at the time, although downgraded by his detractors, was quite important, including deails that led to the discovery of 52 microphones, 42 of them still working, that had been "planted throughout the most sensitive parts of our embassy in Moscow."

Impressed for the moment, the principal CIA interrogator, who later became deputy chief of the CIA's Soviet bloc division, wired Langley on June [TEXT OMITTED FROM SOURCE]