President Reagan yesterday dismissed as "much ado about nothing" the continuing questions about how his 1980 campaign advisers received a briefing book prepared for President Carter before the debate between the two candidates.

Reagan, answering questions about the episode for the first time, expressed a desire to "get at the bottom of it."

White House officials said they have no plans to probe further into the incident, but some aides said privately that they are searching for the missing briefing book.

One White House official said Office of Management and Budget Director David A. Stockman had the book last, but apparently discarded it after the 1980 campaign.

The president, questioned briefly during a picture-taking session at the White House, said he had "no knowledge of any such thing" during the campaign, "and frankly I don't think there ever was a briefing book as such."

Three top administration officials told a House subcommittee chairman this week that they knew the Carter briefing material was used by the Reagan campaign before the Oct. 28, 1980, presidential candidates' debate in Cleveland.

White House chief of staff James A. Baker III and Stockman said they had seen the material, and Stockman said he had found it "useful" in preparing for a mock debate he had with Reagan. White House communications director David R. Gergen said the material had been described to him.

A fourth official, CIA Director William J. Casey, said he had "no recollection" of the document, although Baker said Casey gave it to him.

Yesterday, the subcommittee chairman, Rep. Donald J. Albosta (D-Mich.), said in a telephone interview that "there seem to be some inconsistencies" in the letters he received from the four officials.

Although Stockman had a "very good recollection" of the document, Gergen did not, Albosta said. "Baker recalls getting it from Casey, and Casey has no recollection of it at all," he said.

Albosta said the subcommittee intends to "follow up" by asking other officials in the administration about the briefing book. Told of Reagan's comment that the controversy was "much ado about nothing," Albosta responded: "Would he want someone stealing from his White House?"

The charge that the book may have been "filched" from the Carter camp was first raised by Laurence I. Barrett in a new book, "Gambling with History." Barrett did not offer any details about how the book was obtained, and White House spokesman Larry Speakes said yesterday that "there has been no specific allegation of illegality."

Speakes said the president reviewed the letters to Albosta from his aides, but did not discuss the details with them. Speakes described the incident as "history," and characterized it as common practice in political campaigns.

"What I'm trying to indicate is this is the way politics works," Speakes said. Questioned about the propriety of using the material to help prepare Reagan for the debate, Speakes said, "It depends on the level of the material that was received and how it was obtained and what is the common practice in politics."

Speakes tried to minimize the importance of the material and to shift the focus of attention to Jody Powell, who was Carter's press secretary, and Patrick Caddell, Carter's pollster, rather than the Reagan aides who received the documents.

Reagan was asked in the photo session whether he found it strange that his aides could not recall many details of the briefing book episode.

"I don't think it's at all strange," he said. "Honestly, if you think about a campaign and the hundreds of people involved and the reams of paper that are constantly coming in with suggestions, proposals, reports and so forth--look, ask me what paper came to my desk last week and I couldn't tell you."