With his midsummer lead of about 30 points dwindled to a precious few, the challenger has done himself nothing but harm by opening his fall bid to unseat the president with a series of gaffes and miscues.

There is little room for error in tackling an incumbent president, even one who is politically weakened. Yet the challenger uttered statements of confusion, requiring his aides to utter statements of clarification. Carefully crafted speeches were overshadowed by thoughtless ad libs. In one glib swoop, he managed to alienate most of Alabama and the South.

Finally, mirroring the frustration of the challenger's inner circle, the candidate's wife offered him some strong, private advice: "People walk up to you and stick a microphone in your face at the airport or something like that -- don't answer them. Do your thing and leave."

Eventually this challenger -- Jimmy Carter in 1976 -- was able to pull himself sufficiently together. His disorganized organization did the same, after several campaign-rally missteps. Together, they held on to win narrowly.

The cases of Jimmy Carter 1976 and Ronald Reagan 1980 are strikingly parallel: two challengers, trying to topple politically faltering incumbents, who at times seem to be doing more damage to themselves than to their opponents.

And in this time of frustration within the Reagan camp, the Republican challenger and his advisers may find solace, and even some counsel, in the problems that befell the challenger of 1976.

Challenger Carter came out of his convention in the early summer of 1976 with a huge lead in the polls over President Ford. August and early September should have been a time for fine-tuning organization and strategy and keeping steady pressure on the incombent. But the challenger succeeded mainly in increasing the pressure on himself.

There was, for example, Carter's Southern gaffe.

Carter felt the need, in an interview in August 1976, to explain how badly John Connally had slipped in the polls. Connally is ranked so low, he said, that only George Wallace is below him. Carter officials, horror-struck, fell all over themselves to apologize to Wallace, who had just recently endorsed Carter, and whose supporters Carter badly needed to build his Southern base of support.

There was the grain gaffe.

In Iowa, Carter declared that he would end -- "once and for all" -- the embargoes on American grain sales abroad. Later, pressed by a reporter, Carter said that his statement had been "too strong," and that he might institute an embargo if U.S. crops were struck by natural disaster. Republicans saw to it that the story quickly became one of Carter flipflopping. (Indeed, as president, Carter instituted his embargo on grain to the Soviets as a response to the Soviet push into Afghanistan.)

And there was the time Carter, in the first week of the fall campaign, inadvertently stole the spotlight from what was to have been his major effort to attack the president's urban policies in New York.

After his urban speech, Carter chose to remark, in response to a reporter's question, that he would fire FBI Director Clarence Kelley because Kelley had allowed FBI carpenters to build a $355 set of valances for his apartment. Not surprisingly, news reports of the event concentrated on Carter's threat against Kelley and not his attack on Ford.

In that first week of the fall campaign, challenger Carter was running for president like a man on a treadmill, going all-out, yet going nowhere. By the fourth day, the ordeal was clearly taking its toll. Late at night, Carter set out to tell a Chicago crowd, in his standard rally speech, about the importance of preventive health care. Suddenly he stunned even his own staff by beginning to shout to his audience the names of childhood diseases.

"Whooping cough!

"Cholera!

"Typhus

"Typhoid!

"Diphtheria!

"Polio!

"They tried to immunize me against those diseases," Carter said, apparently recalling his own youth," -- and quite often they succeeded."

Last Thursday, as Ronald Reagan was ending his own rocky maiden voyage of the fall campaign, his chief of staff, Edwin Meese, reflected somberly on the week that was.

"We're going to have our ups and downs in the campaign," Meese said. ". . . As long as we're able to do what we want to do, we'll be all right."

Far too often, he conceded, this year's challenger has not been able to do what he wanted to do. He made misstatements about China policy. He overshadowed a major speech by observing that the Vietnam war was a noble cause. He pronounced America into a national economic depression -- a claim even his own chief economist could not support. And he managed, too, to alienate much of Alabama and the South, in his thoughtless desire to somehow link Jimmy Carter with the Ku Klux Klan.

But Meese, a well-respected adviser, believes that these days of political self-flagellation are largely behind them, and that the Republican challenger will once again be making the sort of news he sets out each day to make.

At the very least, Meese is looking to improve Reagan's batting average during the next road trip. "If we get positive stories three days out of four, it won't be all that bad," Meese says.

To that end, the Reagan strategists have come up with a campaign plan that amounts to, basically, a thought-for-the-day approach to presidential politicking.

The best way to see to it that the former actor does not steal the spotlight from his own story or step on his own best political lines is to have Reagan serve up just one central message each day, the Reagan officials concluded in a series of recent meetings aimed at trying to put their campaign in order.

So it was that, on Thursday, Reagan began his day in Jacksonville with a luncheon speech that was a harshly worded attack on the Carter administration for having made public details of the "Stealth" project for making airplanes invisible to radar.

And the candidate then left his luncheon audience and went out to a downtown park, where he repeated the same speech to a rally crowd. And that evening, in New Orleans, he gave the same speech once more. For the entire day, Reagan succeeded in doing what he hopes to do for the entire campaign: he kept the incumbent on the defensive.

Television networks -- which are the candidates' prime campaign vehicles -- will concentrate on only one Reagan campaign story each evening news show. So it makes sense, the Reagan officials concluded, for Reagan to serve up his messages like vitamins, one a day. It is their best hope of putting a prompt end to the early-season gaffes that plagued 1980s challenger, as they did 1976s.

As Meese tactfully explains:

"There is a desire to not have a confusion of themes. It is a desire on our part not to make it too hard for the press to get the message across."

EPILOGUE: No plan is foolproof. Thus, last Thursday, even as the Reagan men were implementing their all-out plan of damage control -- with senior advisers on board the campaign plane to see to it that there were no unforseen occurrences -- the Reagan plane was hit by a minor unforseen occurrence.

From faraway Wall Street came rumors that Reagan had suffered a heart attack, rumors which were completely unfounded and unfair, yet caused stock market prices to drop.

All of this caused reporters to question Reagan, who looked as healthy as ever, about the state of his health.

At first Reagan noted, with understandable pique, that if this rumor was someone's deliberate campaign plant, "it's a pretty sleazy thing." But later, he was able to dismiss it with a joke, telling reporters, "Well, if any of you want to make some money in the market, just let me know."