It took Washington three weeks to wake up to what could be the most gripping story of the year, the possibility that the famous Carter-Reagan debate of 1980 was not a fair fight, that Ronald Reagan walked into the biggest gamble of the campaign with loaded dice in his pocket.

The initial reaction to the disclosure by Laurence Barrett in his book, "Gambling with History," that someone in the Carter camp had stolen the then-president's debate briefing book out of the White House and passed it to the Reagan camp was, "So what else is new?"

That doesn't mean that the town has retroactively bought President Nixon's "everybody does it" Watergate rationale. It has more to do with people's vivid memories of the momentous encounter between incumbent and challenger on Oct. 28, 1980.

The collective folk judgment is that Reagan's demeanor won the day, that Carter's hope of unmasking him as a dangerous, ignorant warmonger was doomed when Reagan pranced on stage, all glossy cordiality and charm. By contrast, Carter seemed stricken with nerves, so tense that he looked affronted when Reagan bounded over to shake hands before the hostilities began.

When Reagan burst out with that human, colloquial, "There you go again"--just the way someone would in a family argument--the electorate was disarmed, the sophisticates say.

So Washington knew better than to get excited about tedious, pilfered details in a briefing book. It embraced Reagan's "much ado about nothing" dismissal even before he uttered it.

It took the denials of the campaign officials, now on high perches in government, to send the antennas flying up and the get the juices flowing.

The explanations were vintage and replete with contradictions, blanks, hedgings and outright evasions. They gave off an unmistakable aroma of sweat.

The tattered reminiscences were prompted by the inquiries of an obscure chairman of an obscure House subcommittee. Rep. Donald J. Albosta (D-Mich.) was the only member of Congress who would go near the charges being pressed by furious former Carterites, led by former press secretary Jody Powell. Albosta asked for answers in writing. He got back a rich harvest of preposterousness.

Take, for instance, the creakingly careful explanation from the ultra-professional James A. Baker III, the generalissimo of the Reagan debate forces, who is now White House chief of staff.

Having admitted that he got the book from campaign chairman William J. Casey, who is now director of the CIA--"I do remember briefly seeing a large loose-leaf bound book, I believe in a black binder"--he slips immediately into the damning passive voice, "that was thought to have been given to the Reagan camp by someone with the Carter campaign."

" . . . That was thought to have been given" commands the attention.

"Thought!" By whom?

And, more importantly, "Given!" By whom?

Baker reportedly did not ask.

Casey says that he remembers nothing of what anyone would think was a delirious moment in the campaign.

He has "no recollection at all" of "a set of papers, which laid out the Carter debate plan." Well, anyway, not of a "black book," he said in an amendment issued later by the CIA.

David A. Stockman, who played Carter in the debate rehearsals so brilliantly that he was made director of the Office of Management and Budget, admits to having seen the book, which, he adds, in a wonderfully irrelevant aside, was not "classified."

Nobody ever said that it was. The allegation is that it was stolen.

He at least admits the screamingly obvious. He admits that the book was "useful."

David R. Gergen, a debate coordinator, who is now White House director of communications, differs. His recollection of the debate book may be "hazy," but he's very clear about one thing: "The so-called Carter debate book was inconsequential in the preparation of debate materials used by Gov. Reagan."

Reagan finally stepped up to the plate in person and knocked his alibi out of the park, although it turned out to have a string on it, too.

"Frankly," he said, with a let-a-man-at-it air at a White House photo session, "I don't think there ever was a briefing book, as such."

"As such?" As what, then?

The Carter forces have taken care of the non-existence question by issuing copies of it far and wide to all interested parties, including the White House legal office, which requested one.

If Reagan in 1980 had anything like it in his possession, it's no wonder he had wings on his heels the night of the debate. The 300-page compilation of "Debate Briefing Materials" told everything he needed to know about Carter's strategy: not just what Carter would say, but what he would reply to what he thought Reagan would say.

Carter was wearing a blue suit. Reagan was clad in armor. Every day now, more people will want to know who is tailor was--and why.