GEORGE BUSH broke a big promise last week -- you remember, that oath he took not to ask for new taxes. Democrats were gleeful. Conservative Republicans were furious. But many of his predecessors would have taken it in stride. For presidents, broken promises are like yesterday's poll results. You try to forget about them.

Among presidents, only Jimmy Carter promised "I'll never lie to you." Bush never promised that. Nor did he promise to keep his promises. And if a man can change his position on abortion and Reaganomics (and finesse his stand on leave-time for parents of newborn children), why expect consistency on something so mundane as taxes?

Besides, Bush's was certainly not the most important presidential pledge ever broken. In this century alone, three presidents -- Woodrow Wilson, Franklin Roosevelt and Lyndon Johnson -- made and broke what most voters took to be promises to keep us out of war.

Sometimes, we even praise politicians for changing their minds. Sure, those who liked the politician's original position inevitably speak of "betrayal" and "deceit." But those who agree with the new position usually praise the turncoat's "statesmanship" and "growth." The liberal Republican Ripon Society tried the statesmanship defense last week, praising Bush for "great political courage." There's precedent for this, too: Few now begrudge Jefferson for breaking with his opposition to a strong central government when he purchased the Louisiana territory from France, thereby doubling the size of the country.

Bush himself said at his Friday news conference that in contemplating "the slings and the arrows" now being directed at him, he "went back into history" for some comfort and found Abe Lincoln -- who freed the slaves despite campaign statements that he wouldn't. One can imagine his aides are doing the same thing this weekend, rummaging through the past as they brainstorm ways of getting people to stop talking about Bush's lips.

They are unlikely to do better than Sam Rosenman, FDR's speechwriter and adviser.

During the 1932 campaign, Roosevelt repeatedly denounced Herbert Hoover's reckless spending. In a speech in Pittsburgh, FDR went so far as to promise a balanced budget. When it became clear during his first term that a balanced budget was the last thing the New Deal would produce, Roosevelt is said to have turned to Rosenman for advice on what to say.

Rosenman had it all figured out: "Deny you were ever in Pittsburgh."

Unfortunately for Bush, his tax promise is on videotape for Democrats -- and network producers -- to replay as often as they like between now and 1992. Bush can't deny that his lips were ever in Pittsburgh.

What Bush can do is to claim that when it comes to broken promises, he is in what most historians -- especially Democrats -- would regard as good company.

"While I am talking to you mothers and fathers, I give you one more assurance," FDR told a cheering crowd at the Boston Garden on Oct. 30, 1940, shortly before Election Day. "I have said this before, but I'll say it again and again and again: Your boys are not going to be sent into any foreign wars."

According to Wendell Willkie's biographer, Steve Neal, the Republican presidential candidate exploded when he heard Roosevelt's speech on the radio. "That hypocritical son of a bitch!" Willkie shouted to to his brother. "This is going to beat me!"

In making, and breaking, his pledge, Roosevelt was only following the example of the Democratic president in whose administration he had served, Woodrow Wilson.

With World War I raging in Europe, Wilson campaigned in 1916 as the peace candidate. "He kept us out of war," was his slogan. "You Are Working -- Not Fighting!" one Democratic advertisement declared. "Alive and Happy -- Not Cannon Fodder!"

If the Republicans won, Wilson declared, "we shall be drawn in one form or other into the embroilments of the European war." As for himself, Wilson said: "I am not expecting this country to get into war."

Wilson won a narrow victory -- and the next year, the country was at war.

Lyndon Johnson did no better. In 1964, the Democrats again cast the Republicans, who had nominated Barry Goldwater, as the party of war. "We don't want our American boys to do the fighting for Asian boys," Johnson said in a statement that haunted him for the rest of his life. ". . . we don't want to get tied down to a land war in Asia."

Talking about "Democrat wars" is favorite Republican fare, as Bob Dole reminded the country during the 1976 campaign, and we can expect the president's defenders to recall such broken promises in the coming months.

But if there are precedents for Bush's about-face, they don't provide him with much comfort. The Vietnam War, after all, destroyed Lyndon Johnson's presidency. Roosevelt had Pearl Harbor to blame for breaking his pledge.

And the language politicians use in making their promises really does matter. Wilson and Johnson, for example, sought to fudge. Note Wilson's "I'm not expecting" and Johnson's "we don't want" formulations.

Had George Bush simply said "I'm not expecting to raise taxes," or "we don't want to raise taxes," he would have few problems today. But saying it that way wouldn't have helped much in the campaign; even Michael Dukakis said he didn't want new taxes. It was the sheer force of Bush's language and the Clint Eastwood swagger in his words that make them irresistible as targets today -- and made them attractive as campaign rhetoric two years ago.

Recall the original version of the lips pledge, in his acceptance speech two years ago at the Republican National Convention. "And the Congress will push me to raise taxes, and I'll say no," he said, "and they'll push, and I'll say no again, and they'll push again. And I'll say to them: 'Read my lips: No new taxes.' "

Peggy Noonan, who wrote Bush's acceptance speech, reported in her memoir that Bush aides kept trying to take the "Read my lips" line out of the speech. "I kept putting it back in," she said. "Why? Because it's definite. It's not subject to misinterpretation. It means, I mean this."

Precisely.

Not all broken campaign promises are created equal. Some of them really matter and some don't.

One that didn't matter was Richard Nixon's 1968 assertion that he saw no "reasonable prospect" that he'd recommend a guaranteed annual income. He eventually did just that, but the promise was incidental to the Vietnam-era campaign.

Bush's pledge mattered. His tax stance was central to both his nomination and his election. Many contend that Bush decisively beat Bob Dole in the New Hampshire primary because Dole refused to sign a "no tax" pledge and because Bush ran a hard-hitting television commercial accusing Dole of "straddling" on the tax issue. Dole has so far resisted the temptation of asking who's straddling now.

Harry McPherson, a Washington lawyer and former LBJ aide, suggests a way of testing the egregiousness of any broken pledge. "I think the test should be whether a candidate actually believed what he was saying at the time he said it," McPherson said.

McPherson doesn't pretend to know if Johnson expected the escalation in Vietnam when he made his "American boys" statement. He thinks Johnson still had hopes of making a deal with Ho Chi Minh. As for Bush, McPherson is inclined to believe that the president knew he would have trouble keeping his promise on taxes. But McPherson adds graciously: "I suppose if I can give Johnson the benefit of the doubt, I ought to do the same for Bush."

For the record, Bush himself insisted on Friday that he meant what he said when he said it. "I was convinced I could stay the course," he said. But he then blamed the press for not probing his tax position closely enough two years ago. "I don't think anybody did such a good, penetrating job of questioning," said Bush, who held few campaign press conferences. Was he suggesting that he had a secret revenue-raising scheme all along and that the sluggish press never uncovered it?

If he really did have early doubts, he could have avoided digging himself into such a deep rhetorical hole. Other politicians have figured ingenious ways of avoiding the very specificity that Noonan found so attractive in the "lips" phrase.

When Dwight D. Eisenhower ran for his first term in 1952, he expected that popular impatience with the Korean War would help elect him. But Ike never really promised to end the war. What he did promise was: "I'll go to Korea," which hopeful voters interpreted as meaning the same thing. Modern transportation being what it is, that was an easy promise to keep. Eisenhower went to Korea -- and also ended the war.

Sure, there are times when even the most vacuuous pledge can come back to haunt a politician. The most famous line from Herbert Hoover's 1928 acceptance speech was this one: "We shall soon, with the help of God, be in sight of the day when poverty will be banished from this nation."

The line became famous because a little more than a year after it was uttered, the country slumped into the Great Depression. If Hoover had enjoyed the services of modern-day political consultants, they would no doubt have claimed that Hoover had left himself an out: They would have blamed God for not helping the president enough.If there is redemption for Bush, it may lie in the one attribute that history teaches us not to associate with presidents: Candor.

McPherson, for one, thinks the most remarkable thing about Bush's performance last week was not that he changed his mind, but that he didn't explain why. "Lyndon Johnson would have been out there with charts and a blackboard and he would have written all over the blackboard and he would have bored everyone to death explaining why he did what he did," McPherson said.

Bush's initial reluctance to face the music was no doubt an effort to avoid facing television cameras and producing yet more incriminating videotape. And some think he may be trickier than we give him credit for. His language -- he called for "tax revenue increases" -- is about as fuzzy as Noonan's "read my lips" phrase is specific. This time, at least, he left himself an out.

When the president finally went public on Friday, he tried hard to argue that he faced a new, unanticipated situation. He cast himself as someone with enough courage to change his mind. And in fairness to Bush, many of those who now happily assail him for breaking his campaign promise are the very people who criticized him so fiercely for his stubbornness in not breaking his promise. If everything works out fine for the economy, most people will probably forgive Bush his fiscal unfaithfulness. After all, two-thirds of the electorate said after the election that they expected him to break his tax vows and less than a fifth said they would hold his doing so against him.

But he would be mistaken to assume that he's out of the woods because so few voters believed his promise in the first place. The logic of this position is to hold that a lie is not a lie if no one believed you in the first place. This view represents the ultimate cynicism -- precisely the sort of cynicism that leads voters to conclude that elections don't really decide anything important, because candidates never speak truthfully anyway.

The problem with what Bush did is not that he changed his mind, but that he continues to leave the appearance that his tax vow was really a contrivance all along. This, for example, was the advice he gave Republican congressional candidates opposed to new taxes. "Advocate what you believe, and what you tell your constituents what you'll try to do, and then just try to stay a little bit open-minded. . . ." In other words, say one thing before the election and be prepared to do something else afterward.

If he wants the slings and arrows to stop, the president still needs to say more about what happened and more about why he changed his position. Otherwise, how can he expect anyone to believe he means what he says about anything?

Candor has an additional virtue: It can allow politicians to display a becoming, self-deprecating sense of humor.

When Ronald Reagan was governor of California, he said he would never approve of witholding state income taxes from workers' paychecks. He said he was "set in concrete" on that position. Later, in a compromise with the Democrats, he agreed to do just what he said he'd never do.

Reagan eschewed elaborate rationalizations. "The sound you hear," he told reporters, "is the sound of concrete cracking."

If Bush comes clean, maybe the former president will help him come up with some jokes about lip-reading.

E. J. Dionne is a reporter for The Washington Post.