If you're a Jimmy Carter fan, you are entitled to feel pretty good right now. The same polls that only last autumn were being reported as Carter's political obituary are now confirming the president's immense popularity.

Carter, according to all surveys, is about to crush Edward Kennedy's now poverty-stricken challenge in places like Maine and New Hampshire -- both only a good cab ride from Harvard Square.

Carter is, if anything, more impressive when matched against any of his probable general-election opponents. The principal Republican challengers -- George Bush, Ronald Reagan, Howard Baker and John Connally -- trail Carter, respectively, by 32, 37, 37 and 54 percentage points in the most recent national poll. A 32-point lead is terrific just about anytime; but in a national election -- where a single point represents 815,000 individual voters -- it is absolutely outstanding.

What these numbers mean is that if the presidential balloting were held today, Jimmy Carter would bury his strongest Republican opponent by more than 26 million votes. A 26-million vote victory is beyond a landslide; it's political earthquake.

For Carter supporters, even the latest bad news from Capitol Hill -- allegations of bribery and payoffs to congressmen -- does not really damage the president. The one continuing Carter soft spot in every poll has concerned his inability to deal with Congress, to get things done. Maybe the public will now surmise that this is why Jimmy Carter has had some trouble on Capital Hill if payoffs are what's required to get things done. Nobody has ever seriously questioned his honesty or integrity, you know.

But still, for the Carter supporter there are problems that will not go away and that, when considered, produce uneasiness instead of confidence.

Take the Kennedy situation. If, as conventional wisdom now predicts, Jimmy Carter does trounce Edward Kennedy in New Hampshire on Feb. 26, only two possible results can occurr: one is that Kennedy will get out of the race; the other is that, some how, he will stay in. If Kennedy withdraws, then press and public attention will quickly switch from Candidate Carter, the victorious, to President Carter, the embattled. carter will get very little time in the sun for achieving his most remarkable triumph, the conquest of Sen. Kennedy. Instead, the stories that are written will probably concentrate on Kennedy's failure and future rather than on Carter's victory.

Unfortunately for Carter people, if Kennedy does retire from the fray, he will not take inflation with him. With the focus again on President Carter, there could quickly develop a growing public belief that he was far more formidable in whipping Kennedy than in whipping inflation.

It might even be better for Carter politically if Kennedy were to remain in the race after his anticipated loss in New Hamsphire. Except that there is that nagging 1980 problem of "volatility." What if the polls start to slide with Republican criticism or, more probably, with new and unpredictable international developments that do not help the president? Would that be followed by a Kennedy upset victory someplace and result in the long, bitter, divisive campaign that had been predicted? Kennedy out can mean problems and so can Kennedy in.

Right now, the best bets are that the economy and defense will dominate the national agenda next fall. Both of these can contribute to the Carter fan's sense of unease. The simple fact is that the American people do believe the Republicans will do a better job of holding down taxes, controlling government spending and fighting inflation than the Democrats. In this election, for the first time in his remarkable political career, Jimmy Carter will not be the perceived instrument of change. He is the incumbent. His record, his stewardship will be attacked and must be defended by him and his supporters. And those supporters also know that Carter, like the overwhelming majority of political candidates, is not nearly so attractive or effective on the defensive as on the offensive.

Republican platform speakers are somewhere, right this minute, rehearsing their 1980 lines: What about the balanced budget Carter solemnly promised? And "the Ford interest rates -- the highest since the Civil War" as well as the "terrible, unacceptable Republican inflation rate of 6 percent " -- both of which have gone considerably up instead of down in the last 46 months?

While Kennedy, on Carter's dovish left, is unable to mount an effective case against the president's turn-around on the Soviets and the defense budget, it is hard to believe that any Republican nominee, in the fall, would not have a longer, stronger and more consistent record of skepticism toward the Soviet Union than Carter.

Within the Democratic coalition and within his own campaign, President Carter could face more problems. Because he was really an outsider, Carter does not have the close ties with labor or other traditionally liberal groups that, for example, a Hubert Humphrey had. Between Carter and the leaders of these constituencies, there are no shared political foxholes about which the reminisce or long marches together to recount.

So when, and if, Carter moves further toward austerity in economic policy, he will not be able to mollify these people with a quick call or a quiet drink. And they will probably, in the fashion of the times, go public with their opposition, because for three years the Carter administration has been most responsive to public criticism.

All of this could hurt in the general election and put more pressure on the Carter campaign staff, which for the first time has at the top people whose fate, fortune and future are not tied directly to the political success of Jimmy Carter.

Even a good campaign has more tension than a bad marriage, and that tension will mount as November nears and as, almost inevitably, Hamilton Jordan, the Judge Crater of this administration, reemerges to take full control. Despite the glad tidings of Dr. Gallup and Mr. Harris, things all of a sudden don't look quite so rosy.