The Central Intelligence Agency's investigation of the rifling last year of a congressional committee's files by one of its officers was aimed primarily at getting the CIA off the hook, according to informed sources.

"They investigated it to get out of it themselves, not to find out whether somebody else was involved," said one knowledgeable source.

The Washington Post reported yesterday that the most sensitive files of the House Assassinations Committee had been rifled last summer by a CIA liaison officer who had been assigned to help the committee.

The CIA responded by saying that the officer in question, Regis T. Blahut, had been dismissed. CIA spokesman Herbert Hetu said the agency was "satisfied" that the incident had been simply "a matter of curiosity" on Blahut's part.

Sources close to the committee sharply disputed the CIA's assertions. One said "the circumstantial [evidence] is overwhelming" that more than "curiosity" was involved.

CIA officer Blahut, this source said, "went into a room where he wasn't supposed to be without one of our officers being present."

There, the source said:

"He opened a safe, and pulled out a drawer.

"He took a ring-binder notebook out of the drawer, he ripped a plastic case out of the notebook and he took a picture out of the plastic case.

"He fled when he heard a noise, and then he lied about it."

According to this source, both CIA Director Stansfield Turner and CIA Deputy Director Frank Carlucci were informed bluntly by the committee's chief counsel, G. Robert Blakey, of what the committee regarded as the shortcomings of the CIA inquiry.

Heut denied this. In a telephone interview yesterday, he also denied that the CIA had conducted a shortsighted, self-protective investigation. "We did check outside and inside [the agency]," he said.

Hetu also maintained that Blahut had every right to be in the room where the safe was located.

The rifled safe was reserved for physical evidence from the Kennedy assassination and, at the time, contained at least the grisly autopsy photos. The safe containing CIA records and other materials that Blahut was supposed to safeguard was in another room, sources said.

Committee staffers discovered the incident one afternoon last July after a committee lawyer had gone into the room, with Blakey's permission, to inspect some of the autopsy photos. He left the room briefly to speak with Blakey and returned to discover that one of the notebooks he had not touched was out of place.

"If it were just curiosity, why should you have to take photos out of an unused book in order to see them? Why not just look at them?" one source said.

As for Blakey, sources said, he had always been "paranoid" about the possibility that some of the gruesome Kennedy autopsy photos might get out and destroy the committee's reputation.

"No one who has seen those photos would have any doubt that they should not be made public," one source said. "The one thing that would have done us [the House Assassinations Committee] in would have been for those photos to be publicly released. We were never satisfied that someone else wasn't involved."

Of the CIA's Investigation, one source said, "all they investigated was whether he [Blahut] had any connection with the agency [in doing what he did] . . . They asked [Blahut] on a polygraph [examination] whether he had any connection with the agency in doing what he did. And he passed when he said he didn't have any connection. But they didn't ask whether someone else had authorized him to do it."

Turner enunciated the agency's view yesterday afternoon in one of his "Director's Notes" to all CIA employes: "A media report today suggests that there was something sinister involving the agency and the files of the House Assassinations Committee. I want to assure you that this is simply not the case. Our investigations revealed an error in judgment by a contract employe as a custodian for CIA material with the committee. He acted alone and out of curiosity and was dismissed."