The Central Intelligence Agency, which has recently thrust into the limelight its efforts to prevent leaks of national security information, has classified as "confidential" the details of a mock Ku Klux Klan meeting at the agency that is now being dismissed as "a tasteless joke."

The incident occurred around Christmas last year when a CIA officer and an outside consultant walked into a room called the "Ruffing Center" in the headquarters' computer services area, sources said.

According to the sources, the two were astonished at what they saw: There were perhaps 15 to 20 people in the room. Some wore cone-shaped hats made out of computer paper and they had a black man up against a wall. They appeared to be intimidating him.

After a few moments, the sources said, they let the black man go. The two interlopers asked what was going on. According to the sources, the two were told, " 'This is a Klan meeting. We're connected with the Baltimore Klavern,' or something to that effect."

Thus began what one intelligence official has described as "a tasteless joke" that got out of control. But the incident and subsequent remarks were taken seriously enough at the time that they led to complaints to the CIA inspector general and an internal investigation, and finally to inquiries from the Senate Select Committee on Intelligence.

Several weeks ago, the CIA submitted a report to intelligence committee Chairman David F. Durenberger (R-Minn.) and Vice Chairman Patrick J. Leahy (D-Vt.) but classified it as "confidential."

"I can't talk about it," Leahy said when asked about the report. "It's classified."

Durenberger said he was not familiar with the details. He said as he understood it, "There was something there, but it wasn't what it was cracked up to be."

According to the sources, the "joke" became an extended one. They said the outside consultant was asked, possibly in a subsequent discussion, whether she wanted to participate in KKK activities. She had put a note on a CIA bulletin board earlier saying she was a seamstress willing to take on some work, the sources said, and one of the putative Klansmen told her they needed robes or costumes.

The consultant, the sources continued, was also told that the purpose of the group was "to keep blacks and ethnics" -- which she took to be a reference to Hispanics and Asians -- "in their place."

The CIA officer with her also took the matter seriously, the sources said, and lodged a complaint. Later, when the officer asked about the status of his inquiry, he was reportedly told not to worry, that the targets of his complaint were no longer "doing anything that's dumb."

That was interpreted by some to mean that the supposed KKK unit was no longer holding meetings at agency headquarters, but CIA and Senate officials are emphatic in saying there never was a real Klan "meeting" to begin with.

"We are completely satisfied that there is not any KKK klavern or unit out there," intelligence committee aide David Holliday said for Leahy.

Under a 1982 executive order issued by President Reagan, "Information may not be classified . . . unless its disclosure reasonably could be expected to cause damage to the national security." The confidential stamp "shall be applied to information, the unauthorized disclosure of which reasonably could be expected to cause damage to the national security."

CIA spokeswoman Kathy Pherson said, "About all I can do for you is tell you the allegations about KKK activity were made in a Vienna Va. newspaper . . . . I think it was sometime last month. The allegations are completely false. They were investigated by the CIA's inspector general and shown to be without foundation."

The allegations, however, were not aired first in a Vienna newspaper. They first appeared in an article by former CIA official Victor Marchetti in the May 12 edition of Spotlight, a right-wing weekly tabloid published in Washington. Marchetti maintained that the Klan "meeting" was real and that the CIA was apparently "attempting to stonewall the story" until it could "come up with a plausible and hopefully acceptable explanation."

Bernard F. McMahon, staff director for the intelligence committee, said he understood that the incident took place "in a small office where everybody is friendly with everybody else. I don't remember what triggered the activity, but it was something innocuous. It was not a slur or a fight or anything."