More than a year after they were made, the CIA is denying allegations by a former CIA officer that the agency fabricated evidence in the early 1960s to help prove that the war in South Vietnam was being fueled by North Vietnam and to help set the stage for heavy U.S. involvement.

The allegations were made by Philip Liechty, a former case officer in the agency's top-secret Directorate for Operations who spent 15 years with the CIA. They were reported in The Washington Post on March 20, 1982.

At that time, a CIA spokesman was asked for comment on Liechty's claims and said only that "it is not our policy to comment on such allegations."

Liechty said that early in his CIA career, he inadvertently came upon agency documents of proposed operating plans to fabricate evidence of outside support for the Vietcong guerrillas of South Vietnam.

One such plan, he said, involved an elaborate operation to print anti-American Vietnamese postage stamps and have them placed on letters that would find their way into the European and western press.

Another plan involved loading captured communist-bloc arms collected by the CIA onto a coastal boat in Vietnam and then staging a firefight in which the arms-carrying boat would be sunk and displayed to the press.

At the time of the interview last year, Liechty said that he was obviously unable to produce the documents he said he had seen in the files about 17 years earlier or several sheets of postage stamps that he said he had seen in the file and held in his hands.

CIA spokesman Dale Peterson now says that the agency has made a thorough search of its documents and interviewed other officials and that there "is no evidence that CIA ever fabricated that stamp. I say this with 99 percent confidence because there is no trace of this being done."

The CIA, he added, also "did not fabricate that stamp for domestic U.S. consumption." A copy of the Vietnamese stamp that Liechty described appeared on the cover of Life magazine on Feb. 26, 1965, two days before the Johnson administration published its "white paper" on the war called "Aggression from the North." Peterson says the CIA had nothing to do with that magazine cover.

Asked if the CIA used the postage stamps and distributed mail with them, even if the agency did not print the stamps, Peterson said:

"We are not saying we never used that . . . . When talking about use of the stamps and other things, right or wrong, we are not commenting. That is just a matter of policy. We can't comment if we got them in Vietnam and used them for something."

Peterson said that agency policy not to comment on allegations about operations should not be construed as confirmation or denial.

Peterson also said there is "no evidence" to support Liechty's claim about the arms-laden boat. "We are talking about 1965," he said, "and that was a long time ago. But we interviewed people who should have known and came up with zero on that."

Asked about the CIA denials, Liechty said he sticks to his original claims.

"It is possible," he said, "that they could have used either forgeries or the original Vietnamese stamps. You just really couldn't prove which stamps actually went on the envelopes.

"But they did have the stamps, they were there and they were using them in the way I said. There is no question whatsoever that they did it. They had huge quantities in sealed, cellophane envelopes. My recollection was that they were printing them and that the documents that I read discussed the options of printing them," he said.

On the boat incident, Liechty said that while he cannot be sure that the CIA staged the specific incident pictured in the "white paper," "it matched and fit with what I knew they were trying to do and had approved. I was describing a series of similar operations that the agency was conducting, and I stand by that firmly."

Interest in Liechty's initial interview was revived recently with publication of a book entitled "Deadly Deceits." It was written by another ex-CIA agent, Ralph W. McGehee, who repeats Liechty's claims based on Liechty's interview with The Post.

Also, Linn's Stamp News, a trade newspaper for stamp collectors, has published two articles in recent months in an effort to clear up whether the postage stamps were forgeries. The newspaper concluded that the stamps were probably not forgeries.