Five-thousand feet above this little farm town, the twin-engine Piper Cherokee jerked to the left and spun into a sickening dive through the clouds. The fertile fields of central Illinois raced frighteningly upward.

"Oh, sorry about that," Terry Bruce said calmly, from the pilot's seat, his words muffled by a yawn. "I just dozed off for a second there, and my left arm hit the wheel. It happens some nights whem I've been flying the district all day."

For Terry Bruce, the amiable Democrat who flies his own campaign plane around east-central Illinois in his effort to win a seat in Congress, untimely fatigue at high altitudes is just one of the minor perils that accompany a political campaign.

In the 13 months since he declaredhis candidacy for the open House seat here in Illinois' 22nd district, Bruce has discovered that the path to high office is studded with detours through low comedy, tedium, frustration and fatigue.

He has endured uncounted missed meetings and staff foul-ups. At one parade, he was attacked by a horde of kids trying to steal the candy he was passing out.

Things could be worse, of course. For Bruce's Republican opponent, Dr. Dan Crane, they often are. Terry Bruce, at least, loves to go out campaigning, Crane an introverted dentist, hates it - but anyway has to suffer all the indignities that befall a candidate.

This is not to say that the 22nd's campaign for Congress is being played out to the tune of a funeral dirge. Both men have found remarkable reserves of patience and energy during the race, and they still display good spirits most of the time. The race is close, and the thought of victory, of a seat in Congress, is a heady tonic for tired candidates.

Still, the campaign has been more trying than either man expected.

This is partly due to its extended duration, Cexpected.

This is partly due to its extended duration. Cs full time since September 1977, when the 22nd's popular incumbent congressmen, Democrat George Shipley, shocked the district by announcing he would not seek reelection.

The drawn-out battle has taken a toll on Crane, whose dislike for pressing the flesh and exchanging inanities with people he's never met has grown progressively over the months.

In a tired moment last winter, Crane compared himself with a puppet at the hands of his campaign staff. "They pull the strings," he said then, "and I say, 'I'm Charlie McCarthy and I want your vote'."

Today the metaphor has grown starker. "I'm the piece of meat," Crane said at a fund-raiser not long ago. "I'm just a hunk of meat and the people poke their fingers in me to see if I'm fresh. They're going to hang me up in the market from 6 fresh. They're going to hang me up in the market from 6 a.m. to 6 mpaign has also been a disappointment of sorts for Crane, because it has turned out to be something less than the vehicle he had expected for expousing his opinions.

One of his key reasons for running was the belief that the campaign would help him spread the political doctrine he learned from his father, the conservative columnist George Washington Crand IV, and his older brother , Rep. Philip M. Crane (R-III). But the candidate had discovered that most voters won't stand still long enough to listen to his doctrinal dissertations.

"When you're out campaigning you get, what, 30 seconds with the guy?" Crane said recently. "There's no chance to talk about real issues."

Crane does talk about issues on broadcast interviews and in debates, but he doubts that his points get across then either. "Your average guy, with his six-pack sitting in front of the boob tube-no, he doesn't care," Crane says.

The problems are exacerbated by the difficulties of getting around the sprawling district, which has few major roads and as much land area as the state of Maryland. Crane and one or two of his staff aides sometimes take six-hour round-trips to get in one hour of campaigning at the far end of the district.

In that regard, Terry Bruce's tiny red-and-white airplane, which he has been flying since he first won election to the state senate in 1970, is a big asset. It saves hours each day in travel time, and, more important, it is much more relaxing than riding in a car.

"I really need that quiet time," Bruce says, "because my energy is running low. It's hard to get a decent meal in this business - you get coffee and hors d'oeuvres, nothing that has any vitamins. There's not much chance to sleep. And you can't afford to get sick with a campaign on."

Flying is tougher in overcast weather, but Bruce handles the problem with aplomb. "Now we're coming into a cloud," he said cheerfully the other day to a reporter flying with him. "You never know if some son-of-a-gun isn't flying right at us on the other side of that rascal."

That plane came through the cloud unscathed, but the problems on the ground were more substantial. Bruce's staff, a youthful band that is a bit longer on enthusiasm than organization, had fouled up the schedule. He was 90 minutes late for a meeting of campaigh volunteers, and there was nothing he could do but try to make amends to those who had not already left in anger.

For both candidates, the campaigh staff is sometimes more a hindrance than a help. Letters go unanswered because a volunteer lost them. An important contributor is snubbed because a headquarters staffer didn't recognize the name.

In such cases, the candidates have almost no recourse. A rebuke of a key staffer can seriously undermine morale. If a volunteer makes a mistake - how can you fire a volunteer? So both men do a lot of grinning and bearing.

When Vice President Mondale offered to campaign here for Bruce, for example. Bruce asked one of his best workers to organized the trip. Then, a week before Mondale's scheduled arrival, the candidate got an angry call from Washington. The arrangements were so chaotic that Mondale was about to cancel.

Bruce dropped everything to get things back on track, and the vice president's visit was a success.

But for Bruce , the incident was deeply embarrassing.

Finally, both candidates have had to deal with one encompassing difficulty, a problem that creeps up on them at all times of day and then strikes again in the still of night: the fear of losing.

For Terry Bruce and his wife, Charlotte, that problem was exacerbated by his easy victory in the Democratic primary in March.

"If you're going to lose," Charlotte Bruce says, "you might as well lose in the primary and get it over with. When I think that we might have spent a whole year at this and then end up losing - that's pretty horrible. I mean, it's awful."

For Dan Crane, too the stakes are high. Crane comes from a highly competitive family, and three of the Crane boys are running for Congress this year. It would be one thing for Dan Crane to run and lose on his own but defeat now would be a serious letdown for the whole clan.

Accordingly, both candidates have found it impossible to wait for election day to find out if they will win or lose. They have been consulting all sorts of campaign handicappers to ask the ultimate question.