The campaign caravan had been delayed leaving Charley Brown airport, outside Atlanta, when an inexperienced pilot flooded the engine of the six-seat plane and could not get it restarted. "Dammit, don't do that," muttered John Glenn as he watched, visibly restraining himself from taking over the task.

It made Glenn late for the start of the Georgia Peanut Festival parade here a week ago Saturday. Instead of riding down the streets of this south Georgia town in the grand marshal's car, with his own name on the side, he had to clamber aboard the car carrying a festival princess.

No problem. With a celebrity status most campaigners can only envy, the former astronaut was instantly recognized by most of the adults in the crowd. As parents bent to tell their youngsters who the bald, tanned man in the blue business suit was, Glenn tossed off Marine-quality salutes to applauding fans lining both curbs.

There was one skeptic in the crowd. A woman seated on the back of a pickup hollered, as the parade paused momentarily, "Did you really go?"

"Not to the moon," Glenn replied. "I went in Earth orbit, though."

"I told you all he didn't go," the woman said triumphantly to her companions.

Her comment recalled the famous put-down Sen. Stephen A. Young, the tart-tongued Ohio Democrat, administered to Glenn when the astronaut was trying without much success to get started in Ohio politics in the 1960s. "John Glenn never walked on the moon," Young said. "John Glenn never went near the moon. All John Glenn ever did was go around the world in a semi-crouch position."

That was before Glenn got to the Senate on his third try in 1974 and before he set an all-time Ohio record with his 1,633,091-vote reelection victory in 1980, in which he carried 87 of the 88 counties and ran 28 points ahead of Jimmy Carter.

Now, 20 years after he became the first American to orbit the earth, Glenn, 61, is ready to "shoot the moon" by running for president. This week, he will announce formation of an "exploratory committee," already housed in a small office on Capitol Hill, to prepare for the 1984 primaries.

Along with a newly created personal political action committee, the National Council on Public Policy, the Glenn committee will begin the formidable task of raising the $14 million to $16 million he estimates it will take to get to the 1984 Democratic convention and the equally intimidating effort to expand his small, tight-knit Ohio political team into a national organization.

Some Democrats say Glenn is starting too late to have realistic hope of winning. Although he ranks third in the Democratic preference polls, behind Sen. Edward M. Kennedy (D-Mass.) and former vice president Walter F. Mondale, he is light-years behind them organizationally.

Both of them have lists of supporters from past national campaigns, and both have computer tapes of donors to their personal PACs. They are ready, it is said, and Glenn is not. Glenn says, "When I need to be ready, I'll be ready."

The thing to remember about Glenn, a former associate said, is that throughout his years as a Marine fighter pilot, a test pilot and an astronaut, his life literally depended on his step-by-step mastery of complex routines. One does not survive by taking risks in those roles but by following prescribed procedures.

Kathy Belle, his executive secretary, said she hates to fly but will do so with her boss at the controls of his Beech Baron "because he is meticulous about going through the checklist every time we take off; he never skips a step."

Glenn's approach to the presidential race has been equally methodical. The opportunity has been discussed since he scored his landslide in Ohio while Carter was losing the presidency. But throughout 1981, when pressed to get moving, Glenn would reply, "I'm not interested in running just to have it on my dossier. If I run, it's going to be for a cause."

He was far slower than Kennedy or Mondale to condemn President Reagan's program. Although he now ridicules Reaganomics in every speech, he supported the president's three-year tax cut in 1981 because he wanted to "give him a chance." Unlike other Democratic hopefuls, he has not sought an opportunity to reply to one of Reagan's Saturday radio talks.

Even this year, when he saw Reaganomics as a failure and stepped up his own travels in anticipation of a 1984 race, Glenn declined to establish his own PAC, preferring instead to finance his activities with money left after his 1980 race.

All this fed the impression that Glenn would like to be president but not do what it takes to be president. "He's a technocrat," said a fellow senator with presidential hopes of his own. "He really doesn't like politics."

The Washington grapevine buzzes with stories of Glenn's supposed political ineptitude. His reputation as a speechmaker has never recovered from the fiasco of his keynote address to the 1976 Democratic convention, and it was reinforced, according to the grapevine, as recently as the Ohio Democratic convention when Mondale upstaged Glenn on his home ground.

The grapevine says he lacks the staff follow-through to benefit from contacts being made on his travels. "Two of my best people told him when he was here that they'd like to help when he runs," a Midwest congressman said. "They have yet to hear word one from his office."

Generally speaking, Glenn is at his best in small groups, where he can talk seriously -- not rhetorically -- about issues on which he has specialized, including defense, arms control and the Middle East. But even in such a favorable setting, the grapevine says, he can goof badly, as he reportedly did one recent evening at Averell Harriman's house when a question implying that Glenn could not understand the emotions of Israelis prompted him, in one guest's words, to "blow his stack."

All this bad-mouthing would doom the hopes of the average presidential aspirant. But Glenn has advantages as a candidate that make it easy for some kingmakers to ignore such talk.

In the evening, eight hours after the Peanut Festival parade, Glenn was still running late and came into the cavernous hall in the Jonesboro Farmers' Market outside Atlanta to find that Democratic congressional candidate Jim Wood had the 400 people at his barbecue fund-raiser steamed up for the star's appearance.

The introduction came with verbal trumpet fanfares: "A modern-day American hero . . . the Distinguished Flying Cross on five occasions . . . the Air Medal with 18 clusters . . . first in war . . . first in orbit . . . first in the hearts of his fellow Ohioans and first in the heart of the lovely lady whose books he carried to high school and who has been his bride for 39 years . . . .

"John Glenn has a place in American history, and there are many Democrats who want him and his Annie to find a home at 1600 Pennsylvania Avenue . . . ."

The last few words were drowned in cheers, as Glenn stepped forward.

"America may be the land of the free, but Atlanta is the home of the Braves," he began, drawing cheers for the home-town baseball team, then still fighting in the National League playoffs.

"And how about those 'Dogs?" Glenn bellowed, in a reasonable imitation of the natives' salute to the University of Georgia football team, victorious that afternoon.

Aboard the plane earlier in the day, Glenn had told reporters that his reputation as a bad speaker was a bum rap. "You put me in front of a good microphone with a few hundred people," he said, "and I don't concede anything to anyone. I was in Carbondale, Ill., the other night, and I tell you, it was electric."

The Illinois candidate, Democratic Rep. Paul Simon, confirmed that report, and in Jonesboro, Glenn had the crowd with him again. He assailed the "voodoo policies" of Reaganomics, lamented "the longest unemployment lines since the Great Depression" and talked about how interest rates are hurting builders in Clayton County and how bad the prices are for farmers in Henry County.

At the previous stop in Savannah, the references were to Chatham County and Bryan County. Speechwriter Dale Butland inserted the local references in bunches in the day's basic speech text, and Glenn, methodical as always, carefully lined out the used ones after each stop, so he could slide easily into the appropriate names at the next stop.

He quickly outlined his own short-term economic remedy, starting with deferral of the third-year tax cut until "deficits and interest rates come down." For the long term, "defense comes No. 1," he said, "but we can reach new horizons" just by reemphasizing "three things that made this nation great -- education to train our people, research to create new technology and free enterprise that turns that technology into jobs for those we've educated."

He provided a patriotic, upbeat close, quoting novelist Thomas Wolfe on America's promise "to everyone, their chance; to everyone, their shining opportunity." To another standing ovation, he was borne off the platform and into the crowd of autograph seekers.

Annie Glenn, a woman of unaffected warmth who in the last few years has overcome a lifelong crippling stammer and regained the power of speech, spotted a black man and his son at the edge of the crowd. "I saw you out there," she said to Eddie White, "and I'm so glad to meet you."

White held a children's book called "What Colonel Glenn Did One Day," which he wanted Glenn to autograph for the library of the junior high school where he is assistant principal. Mary Jane Veno, who for the last 11 years has tugged at Glenn to keep him on schedule and kidded him to keep him relaxed, escorted White to the senator for the inscription. "He is my man," White said of Glenn. "That book is going to be a treasure."

Many other Georgians feel that way. "We were looking for a national Democrat Jim [Wood] could identify with," said Wood's press secretary, John Knepp. "Georgia is a conservative state, and candidates perceived as liberal as Kennedy or Mondale wouldn't help."

Columbus, Ga., Mayor Harry Jackson, who welcomed Glenn at a campaign stop for congressional candidate Richard Ray (D), said there was "a very warm and favorable response" to Glenn's visit. "His patriotism shines so clearly, just the way he stood at attention when the band was playing 'My Country, 'Tis of Thee.' "

Nancy Newman, Democratic chairman of Chatham County (Savannah), said, "The feedback was very positive. People were impressed with what he had to say; they liked it a great deal. The only complaint was that he does not have charisma, and I think that's crazy. I found him thoroughly delightful and charming."

Support in states such as Georgia is important because Glenn is a northern candidate with a southern strategy. He has little personal identification with causes that traditionally excite urban constitutencies and lost the big Ohio cities in two senatorial primaries against his current colleague, Sen. Howard M. Metzenbaum (D-Ohio).

Although he has good working relations with Ohio labor leaders, many of whom are influential in big international unions that will control the AFL-CIO endorsement decision, his labor record is spotty compared to those of Kennedy or Mondale. And his black support would be minimal compared to theirs.

But in his own analysis, he has more than enough compensating advantages to overcome them.

"However you define liberal," Glenn said in his hotel suite at the end of the Georgia swing, "Teddy is pretty far over on the left. Fritz Mondale is a little less so, and is trying to push more over into the middle. But that's very difficult for him to do. I'm naturally pretty much in the middle, and people know it."

Glenn has concentrated his campaigning on Democrats of his own stripe and has worked particularly hard in the South, the border states and non-big city northern districts.

Looking to 1984, he said he would "not concede to anybody" the curtain-raiser contests in Iowa and New Hampshire. "Small-town Ohio relates to small-town Iowa and small-town New Hampshire," said the graduate of New Concord high school.

But recognizing that those states border on Mondale's native Minnesota and Kennedy's Massachusetts, Glenn said he is focusing on the second Tuesday in March when Florida, Alabama and Georgia may be joined by Oklahoma and Tennessee in a big-stakes regional primary. While Sen. Ernest F. Hollings (D-S.C.) and former Florida governor Reubin Askew (D) offer potential challenges, Glenn said, "I tend to think I would do very well."

Glenn noted that the South will have a larger voice in the 1984 Democratic convention because of population shifts and because the delegate apportionment formula, based on the last three presidential races, will reflect Carter's relatively strong showing in the Confederacy.

A veteran Democrat who has heard Glenn expound this thesis said he is "skeptical that Glenn or his people really know how to get from here to there." He compared Glenn to Sen. Howard H. Baker Jr. (R-Tenn.) as "a perfect general election candidate who couldn't get through the presidential primaries" because his moderation is not exciting to "issue activists."

Glenn concedes that is a risk. "The activists at the convention tend to be considerably more of a liberal bent than the average party member or the average voter," he said. "If that group is seeking a person they personally want, they would not necessarily choose me. If they are seeking someone they can generally support and who can win, they might choose me. Where that puts me, I don't know. I figure I just have to do my best in the primaries and see what happens."

To that end, Glenn is expanding his political team, until now controlled entirely by longtime Ohio associates. His top Senate aide, soon to shift at least partially to the campaign, is William R. White, a Columbus attorney who drafted Glenn's will and joined him full time in his 1974 campaign. White is a cautious, precise man noted within Glenn's circle for his insistence on approving almost every detail of anything involving the senator.

Along with Ohio Democratic chairman Paul Tipps, wealthy Cincinnati fund-raiser Marvin Warner and a handful of others, White has guided Glenn's career.

William Connell, a Washington campaign consultant who broke into presidential politics in 1960 with Hubert H. Humphrey, did the advertising for Glenn's 1980 race and has been White's chief consultant. Judy DiSisti, a fund-raiser for Democratic Senate and House candidates, has just been hired for the "exploratory committee" staff. Tom Boggs, well-known lawyer-lobbyist, has been assisting Glenn with fund-raising contacts and says he will "back him if he runs."

Perhaps the most interesting addition to the Glenn team is Robert J. Keefe, a Washington lobbyist with strong labor connections who worked as deputy to Robert S. Strauss at the Democratic National Committee and then ran the 1976 presidential bid of Sen. Henry M. Jackson (D-Wash.). Keefe, for now, is serving as an unpaid, part-time consultant to the Glenn campaign but may take a larger role.

All of these men are far from idealistic amateurs; they are, in the jargon of politics, "looking for a horse to ride that will get them there."

And there are indications that Strauss, probably the supreme pragmatist among the Democratic operators, is looking the same way. Last week, Strauss' son played host at a private reception for Glenn in Houston.

Although generally regarded as an ally of Mondale, with whom he served in the Carter administration, Strauss has told friends that he could be comfortable with either man.

He has also told them: John Glenn could win this thing.