House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) does not want to talk about Jimmy Carter. He doesn't want to hear about Jimmy Carter. He wants to forget that Jimmy Carter, even though he was a Democratic president, ever existed.

That is, of course, the best news that President Reagan has heard since he began to flounder in the swampy issue of the Carter debate briefing book that somehow made its way into the Reagan camp in the fall of 1980.

Democrats, who think that the affair could represent a light at the end of the tunnel of public esteem that is Reagan's political home, were astonished and dismayed to see their leader throw out the lifeline to the president, who would rather talk about the economy than about a strategy book that he is sure none of his people ever saw.

The speaker gave him the one moment of true ease he enjoyed at a strained news conference Tuesday night.

It came when Reagan was able to say, amid general laughter, that he agreed with O'Neill that "the whole thing ought to go away."

O'Neill spoke earlier in the day with a certain brutality about his erstwhile leader.

"We had an extremely unpopular candidate who would have lost, debate or no debate, briefing book or no briefing book." He says he does not believe that it should be the subject of a congressional inquiry, although one is planned by one of his own, Rep. Donald J. Albosta (D-Mich.), a farmer.

It sounded like a political judgment, but it was probably more of a primal scream.

The four years of the Carter presidency were a purgatory to O'Neill. The dream of a Democrat in the White House turned into a nightmare of slights, mixed signals, alien accents and people who did not play the game of politics as O'Neill learned it in his native Massachusetts.

Apparently, just the sight of Jody Powell, Carter's press secretary, who has been trying to rally Democratic outrage on the matter, was enough to bring it all back to O'Neill. He made it plain that bringing up Carter in any guise, even as martyr or victim of Republican dirty pool, is death to Democrats in 1984.

To rescue Reagan from the welter of corrections, amendments or total withdrawal of previous statements that are coming from White House staff members may not have been in O'Neill's purpose. After all, he has been trying to embolden Democrats to attack the president.

He just wants to be sure that the Republicans do not have Carter to kick around any more in 1984.

Buoyed up and clued in by O'Neill's outburst, the president seized the opportunity to campaign again, subliminally, against Carter.

It is hardly his fault that people like him so much better, he seemed to be saying. Can he be blamed for the fact that even on his White House staff, Carter could not count on the absolute loyalty which he, Reagan, enjoys, and deserves? Is Reagan responsible if the disaffection, so eloquently expressed by the No. 1 Democrat in Washington, was so widespread?

Reagan was reluctant to moralize. He remembers, of course, how Carter's homilies had glazed the country's eyes. He tap-danced around the issue as long as he could.

"Is it stolen," he replied to yet another ethical formulation from Sam Donaldson of ABC, "if someone hands it to you, some disgruntled individual hands to another counterpart in a campaign organization?"

He never did answer his question. To him, the right and wrong of it is as irrelevant as it is to O'Neill.

The White House strategy has shifted slightly in the past week. Seven days ago, the people involved, except for Office of Management and Budget Director David A. Stockman, were arguing that the material--not, mind you, the black strategy book, which Reagan last week said he thought never existed "as such," and which he is now says he is sure none of them ever saw--was of no value. This seemed a little like saying that if you snatch a purse that has only a dollar in it you really haven't snatched it at all. They have rethought that position, it seems, in strategy sessions on the controversy.

"No one that we've talked to that has said that they saw these papers at one time or other--none of them say they ever saw that book that is the strategy book," said Reagan firmly at the outset.

One question was not asked. Why, when he had them all together, did the president not ask which had received the document or documents, from the mole, or moles?

He did not. He has palmed the whole thing off on the Justice Department, while trying to laugh it off in public.

He's doing it with a little help from an unexpected friend. He never thought O'Neill would be in his corner on such a cloudy day.