The former executive receptionist of the 1980 Reagan campaign has told the FBI that papers resembling President Carter's debate briefing materials were delivered to the headquarters by a person she remembers only as "a young, cleancut man."

And, in an unusual move, the FBI asked her to undergo hypnosis to help her identify the man she says brought the documents and the top Reagan official who received them.

The receptionist, Justine Marks, told FBI agents in four interviews that she can recall only that the papers were brought to the Reagan headquarters by a male who was under 30 years of age, according to informed sources.

Marks controlled access to the fourth-floor offices of the top Reagan campaign executives, including campaign director William J. Casey and senior adviser James A. Baker III, who supervised the debate preparations.

Marks confirmed this account during several telephone interviews with The Washington Post. She said that last Thursday she declined the FBI request that she undergo hypnosis even though the FBI agents had told her, "we feel you can provide us with the missing link," she said.

Marks said: "I feel I may be obstructing the investigation but I just can't" undergo hypnosis. ". . . I find hypnosis an unnatural state, like a fortune teller . . . . I would consider this differently if it were a murder, but I think the briefing book thing is Mickey Mouse and I told the agent no."

In eight hours of interviews with the FBI, agents showed her 600 to 700 photographs. But she said she was unable to identify the young man who she says brought the papers to the Reagan headquarters. Nor can she remember the time or day when the papers were delivered, nor the senior Reagan official to whom they were delivered, she said.

FBI officials have been frustrated by the slow progress in the case.

They previously sought permission to give polygraph tests to senior Reagan officials, who have given conflicting versions of how the Carter documents wound up in the files of the Reagan campaign.

Baker, now White House chief of staff, has told investigators he received the Carter debate documents from Casey. Casey, now director of the CIA, has said he cannot recall ever having had the documents and that he would not have forgotten them if they had ever been given to him.

The FBI's decision to ask Marks to submit to hypnosis was approved "at the top" of the FBI, according to an official source. The source declined to say if it was FBI Director William H. Webster who gave the approval, or what role, if any, the Justice Department played in the decision in the politically sensitive investigation.

FBI spokesman Roger Young yesterday said he would have no comment on the matter. He nonetheless said the use of hypnosis with cooperative witnesses who cannot recall details is "a valid, accepted technique." He added, "It has been used many times with superb results."

One nationally recognized expert in the use of hypnosis in investigations yesterday said that the inquiry into the Carter debate documents is just the sort of case in which hypnosis can be useful. Speaking on the condition that his name would not be used, the expert said that most people under hypnosis will provide more specific details of an event, such as names and automobile license numbers.

In several telephone interviews this week, Marks confirmed what she told the FBI and described the arrival of material related to the Carter debate as "a positive recollection."

Marks added, "Of the hundreds of people who passed by me I recall I stopped someone. I don't know who. It could have been someone with the campaign, it could have been a citizen, a politician, even someone with the media and that person had material related to the briefing material for Carter."

Marks said she was not positive the Carter briefing material showed to her by the FBI was identical to the material she saw in 1980, though she said it was similar. She said she was certain the papers received in 1980 were related to the Carter side of the debate, something that would not and did not normally come to the Reagan campaign headquarters.

Asked how she knew the material the young man was carrying was from the Carter camp, she said, "I probably asked him to state his purpose--who he wanted to see and like that."

She said she has tried as hard as possible to recall or further describe the incident or person bringing the material or receiving it but cannot honestly expand on her memory.

"There is a lot I remember," she said, adding: "A lot I don't."