About a week before the Oct. 28, 1980, presidential debate, one of Ronald Reagan's campaign aides reportedly told a close friend, who was President Carter's deputy campaign counsel, that Reagan would win the debate because his aides had a copy of Carter's debate briefing book.

The friend is said to have told this to her boss, Carter campaign counsel Timothy G. Smith, who recalled yesterday that he dismissed the idea as "preposterous" because "the debate briefing books are too closely held at the White House." Smith added ruefully that he did nothing about it.

The incident, aside from being a classic example of how political Washington works, indicates widespread knowledge inside the Reagan camp about its possession of a copy of Carter's thick question-and-answer debate game plan.

The Reagan aide in question, Charles Crawford, was not involved in preparing Reagan for the debate. He worked instead under deputy Reagan campaign manager Robert Keith Gray, who last week acknowledged receiving copies of other Carter documents that he had been told came from a "reliable White House mole."

Crawford's friend in the Carter campaign was deputy campaign counsel Carol C. Darr. Neither Crawford nor Darr could be reached yesterday. But Carter's campaign counsel, Smith, confirmed the account in a telephone interview.

Gray has maintained that the Carter White House documents he received with "White House mole" notations from a Reagan campaign volunteer, H. Daniel Jones, were innocuous. But it was learned yesterday that at least one of the memos Gray received was apparently forwarded to Reagan's campaign plane for use in preparation of the Republican candidate's speeches.

Martin Anderson, the senior domestic policy adviser who traveled with Reagan, said in a telephone interview that he has discovered in his files a copy of an Oct. 24, 1980, memo from presidential advisers Anne Wexler and Alonzo L. McDonald telling Carter Cabinet officials about the September consumer price index figures released that day and what they should say publicly about them.

Anderson said that he has turned over his copy of the memo to the archivist at Stanford University's Hoover Institution, where Reagan campaign files are stored, for transfer to the Justice Department, which is investigating how the Reagan campaign obtained documents and information from the Carter White House and campaign. The memo copy had apparently been forwarded to Anderson even though it had no notation instructing that this be done.

A copy of another Carter White House memo, dated Oct. 10, 1980, and sent by Jones to Gray, carried a typewritten notation routing it to Reagan campaign manager William J. Casey for transmittal to Anderson. But Anderson said that had not yet found that memo copy.

The copy of this memo sent to Gray carried a handwritten note from Jones saying that it came from a "reliable White House mole." It and another memo from Jones to Gray that mentioned such a "mole" as the source of Carter campaign information were provided to The Washington Post by a collector of campaign memorabilia who had found them in a trash bin behind Reagan campaign headquarters here soon after the 1980 election.

The continuing disclosures in the case so far have produced a rather complex picture of a variety of information and documents somehow making their way from the Carter White House into the Reagan campaign. They appear to have created significant conflict in the Reagan administration, with White House chief of staff James A. Baker III and CIA Director Casey making conflicting statements about the Carter debate briefing papers.

Baker has said that he received the papers from Casey. Saying he never saw them, Casey has criticized Baker as "remiss" for not telling other campaign officials about the papers.

Conservatives in the Reagan campaign team and the administration appear to be trying to pin the blame on--and force out--Baker and his allies, who originally joined the Reagan team from the rival Republican presidential campaign of George Bush, now vice president.

William Van Cleave, a conservative Reagan campaign defense expert, said that he recalls having seen the Carter briefing book at the time of the 1980 debate preparations. He said that "the rumor was during the campaign that Jim Baker, David R. Gergen and Stef Halper were taking credit for it."

Gergen, now White House director of communications, was a Baker deputy who coordinated the debate preparation. Halper, now a Washington banker, served under Baker as an issues expert in Bush's presidential campaign and was director of policy coordination in the Reagan campaign.

There are also conflicting accounts about the scope and nature of the Reagan campaign's efforts to monitor the Carter administration. The Post has reported that Casey set up what he once called an "intelligence" gathering unit in the campaign in reaction to fears that Carter would score a political victory by attempting an election-eve rescue of the American hostages in Iran.

A Reagan campaign official working under Casey, Adm. Robert Garrick, organized a group of retired military officers to watch air bases and report any unusual movements of personnel or materiel that could indicate a Carter "October surprise" was under way, although it was never clear what the Reagan campaign would do about it.

Some conservatives have noted that Bush, who was formerly director of the CIA, had attracted a number of ex-CIA officials to support his presidential candidacy. And Halper's name has been mentioned in conjunction with extracurricular political intelligence gathering. Van Cleave said of Halper, "He pretended to have an intelligence shop and a crisis watch room."

Halper responded, "It's preposterous! It's beyond words!"

Halper said that he ran an "operations center" that monitored radio, television, newspapers and wire services on a 24-hour basis. He had five people working three shifts, he said, and every morning he would edit their reports, summarize the day's news for the senior campaign staff and send copies of his news summaries to the Reagan and Bush planes.

He said that his staff also prepared "quick turnaround" research on any issue Reagan or Bush needed material on within an hour or two. He added that they also prepared books providing economic, demographic and political information about each stop the candidates were to make.

Halper said that he had a "network" of "think tank" people from around the country, whom he could call for quick assistance. Among his employes was Robert Gambino, former CIA security officer who quit the agency to join the Bush campaign. Halper said that Gambino did "grunt work," such as monitoring the news media," for the Reagan campaign.

The White House has provided no full explanation of political intelligence operations performed by the Reagan campaign nor of whether it received any classified information from the Carter administration.

Reagan's former national security adviser, Richard V. Allen, has said that he received "innocuous" portions of daily staff reports from the Carter National Security Council staff. He characterized those reports as dealing with "atmospherics" not substance.

Allen has said that he had known that Reagan campaign officials also had a copy of the Carter debate briefing book. But, he said that he had not seen it.

However, Van Cleave, who was Allen's deputy then, said that he did see the briefing book. He said that he believes he saw it in the office that he and Allen shared here. Van Cleave said that it "seems likely" Allen gave him the book and that it "seems unlikely that Allen hadn't seen it, since I did."

Carter's former advisers said that the question-and-answer debate briefing papers obtained by the Reagan campaign were prepared at different times and kept in different places in the Carter White House. That, plus the revelations of the memos that Gray received and those Allen has talked about, have convinced Carter aides that there must have been an on-going flow of information to the Reagan camp from the Carter White House.

Yesterday, former Carter adviser David Rubenstein, who prepared Carter's domestic issues debate briefing papers, said that he is concerned that all of the material the Reagan people had in their files might not be discovered.

"The files of the Reagan archives have not been secured by the FBI," Rubenstein said. He said that it has been left to one employe of the Hoover Institution to decide what documents are relevant to the Justice Department investigation.