Some officials in the Central Intelligence Agency have changed their minds and now take seriously the possibility that Soviet KGB officer Vitaly Yurchenko was never a genuine defector but was a double agent sent to learn about the CIA, redefect and show potential Soviet defectors that going over to the Americans can be hazardous, according to informed government sources.

An operation of that kind could have been prompted by a series of unpublicized Soviet defections last year, which had deeply worried the KGB, according to two well-placed sources, and might have prompted a decision to send a false defector to the CIA.

The CIA is undertaking a detailed analysis of all defectors in recent years. The unpublicized 1984 defections, the sources said, provide a clear potential motive for the Soviets to conduct such a double-agent operation.

Hours before Yurchenko appeared at a Soviet news conference here Nov. 4, a Soviet official indicated to a Washington Post reporter that the entire operation was a "sting" designed to confuse and embarrass the CIA. The official withdrew his characterization after Yurchenko claimed at the news conference that he was kidnaped, drugged and involuntarily brought to the United States by the CIA.

Initially, the CIA assured the two congressional Select Intelligence Committees that Yurchenko was a genuine and important defector, and maintained that position after Yurchenko went back to Moscow.

Sen. Malcolm Wallop (R-Wyo.), a former member of the Senate intelligence panel, wrote in The Washington Post yesterday that "just 48 hours before Yurchenko's redefection, a very high-ranking intelligence official told me he would stake his career on Yurchenko's bona fides."

Sources said that many CIA officials still believe Yurchenko was initially a sincere defector. Either way, officials said, the debate is likely to continue for years.

Intelligence sources acknowledged that the Yurchenko case has revived old fears of a high-level "mole" in the CIA. The sources said that Yurchenko's three-month debriefing by the CIA tended to suggest that he had no knowledge of a Soviet mole high in the CIA or other intelligence agencies. As is often the case in the world of espionage, some have taken this to mean the exact opposite.

The sources, however, said that Yurchenko would in all likelihood not have known of such a high-level plant because his assignments during 25 years of KGB service were almost exclusively as an enforcer, security officer and political indoctrinator, a career that did not involve him directly with the KGB's Directorate S, where knowledge of such a mole would have been limited to those with a reason to know.

Yurchenko's job from 1980 to March 1985 was as head of one of the departments in KGB's foreign counterintelligence branch (Directorate K), according to the CIA. The main task of Directorate K, besides enforcing ideological conformity and physical security of Soviet diplomats and embassies abroad, is penetration of foreign intelligence services such as the CIA. One source said that someone with five years of such work might be an ideal candidate to send as a false defector because he was tough, knew the rules and did not know that much about ongoing operations.

As chief of one of the departments of the total directorate of 200 personnel in Moscow, Yurchenko could not have supervised more than several dozen people. In an unusual biography of Yurchenko distributed by the CIA after he returned to Moscow, he was described as a "general-designate," meaning he was a colonel. Since the KGB hierarchy contains at least dozens of generals and hundreds of colonels, the oft-published suggestion that Yurchenko was the "No. 5 official" of the KGB is clearly incorrect.

Four months before Yurchenko's defection to the U.S. Embassy in Rome, which apparently occurred Aug. 1, he was named deputy director of the KGB department that is responsible for spying in the United States and Canada.

One source said this assignment struck some officials as suspicious, and that perhaps Yurchenko was not really the No. 2 in the conventional sense. Other intelligence sources have speculated that in this department, too, Yurchenko was essentially a security officer responsible for keeping an eye on his associates. A former intelligence officer suggested the fact that he had a brand-new job would have allowed Yurchenko to plead ignorance to many of the questions put to him by the CIA.

The head of the U.S. and Canadian department, according to one source, is a former Yurchenko colleague and superior from the late 1970s, Dmitri I. Yakushkin.

Yakushkin was head of the KGB residence in Washington from 1975 to 1982 and had the rank of major general, according to FBI sources. For five years, 1975-1980, Yurchenko worked under him as the embassy's security officer.

One well-placed source said the CIA now thinks it was possible that Yakushkin selected Yurchenko for a false defection operation. It was an opportunity to strike fear in the hearts of all KGB officers who might think the CIA could provide a safe and secure haven, the sources said.

In addition, Yurchenko's allegations at news conferences, first in Washington Nov. 4 and again in Moscow Nov. 14, that he was kidnaped and drugged by the CIA, allowed the Soviets and KGB to score what they obviously considered a propaganda coup just before the Reagan-Gorbachev summit now under way in Geneva.

U.S. officials have repeatedly insisted that the CIA did not physically mistreat Yurchenko in any way.

The sources said that Yurchenko's presence in Rome supports the possibility that he was a double agent.

"Why," asked one source, "would the new 'deputy' of the U.S. and Canadian department be in Rome . . . . It is only one of the mysteries that may never be resolved."