When the 100,000-pound jet split the rows of corn, first there was heat and a sudden jerk. When the craft hit the trees, its metal burst open with a rasping roar, spilling its mechanical and human contents into the foggy North Carolina woods.

Eastern Airlines Capt. James Reeves and 68 passengers in his charge died suddenly that morning, Sept. 11, 1974. Like all other airline crashes, this one has been poked and shifted, bagged and logged. Committees grouped, boards met, coffins were laid away. The conclusion was that the pilot and crew were not paying attention to their altitude. They simply drifted down to death.

But this official version is now disputed and, unlike other crashes, this one has been resurrected. It's been exhumed because it raises questions of fact, of government policy, of science. How much sleep does a pilot need -- and when?

The North Carolina crash and its causes have been brought up just as the Federal Aviation Administration is about to adopt a new set of controversial rules about a pilot's duty time and rest time.

Fatigue is the issue: fatigue as defined by the rules of the FAA; fatigue as it is experienced by pilots "belly flopping" from motel to motel, city to city; and fatigue as newly redefined by biological science.

At least nine scientists expert in the field of "circadian" physiology -- the daily internal cycles of the body -- have written letters to protest the FAA's proposed rules. The scientists say that the rules are "outmoded," "irresponsible," and "dangerous" to pilot and passengers.

It is not simply that humans need so many hours of sleep every 24 hours, these scientists insist. They need sleep which is truly restful, which does not do violence to the basic biological rhythms of internal organs.

The body has a very large number of physical and chemical functions which rise and fall in regular rhythms every day, including blood pressure, temperature, heart rate, and practically every chemical, hormone, and enzyme so far tested.

This means that the body is virtually a different entity at different times of day and night. The chemicals increase and decrease, and the physical functions speed up or slow down, by a characteristic amount and at a particular time every day.Some change two percent, and some change 1,200 percent. Prolonged interference with these rhythms, scientists now find, leads to deep fatigue, confusion and mistakes.

So far the FAA has refused to comment in detail on these complaints. But the federal air surgeon, H. L. Reighart, who is the FAA's chief medical officer, said, "We have no one with an expertise in that area now."

Both scientists and the FAA agree that fatigue can cause disasters, but scientists now say the fatigue related to these daily biological rhythms is more dangerous than the FAA has realized.

In its rules, the FAA assumes fatigue to be something that occurs during long work shifts, and the longer the shift, the more a pilot will be fatigued. The FAA rules also assume pilots can take their sleep whenever and wherever a block of 10 hours' rest can be arranged.

Scientists disagree. Says Martin Moore-Ede, professor of physiology at Harvard, "The FAA makes assumptions that we now have proved are wrong. A pilot cannot sleep at any time of day and get rested. The rules assume that jumping from night rest to day rest, and back again, indefinitely -- and the rules allow this -- will have not effect. Now there is a massive body of evidence to prove this is wrong."

Until now, neither the FAA nor the National Transportation Safety Board has checked the flight schedules of pilots and crew for the week before a crash -- information which scientists say is critical in knowing whether fatigue in the biological definition was a cause of a crash.

Both the current FAA rules on pilot duty and rest, and the newly proposed ones contain the same assumptions. In the proposed rules, for example, a pilot would be given a rest of at least 10 hours between duty days. The more hours he worked, the more to which he would be entitled.

But since airline computers draw up schedules specifically to squeeze the maximum allowed flying time out of each pilot during a month, the schedules often bear no resemblance to day and night as other workers know them. One three-day round of flying now on Eastern's schedule goes like this:

The pilot leaves Atlanta at 11 at night, lands in St. Louis, Portland, and finally Seattle, arriving about eight hours later. That is seven in the morning by the pilot's body time. Now the pilot is supposed to sleep during the daytime, and fly the reverse trip beginning about 2:30 in the morning, Seattle time. That's 5:30 in the morning by the pilot's body clock.

The same pilot, on returning, may be expected to flop to sleeping nights and flying days in a new sequence.

Scientists say such a schedule may be disastrous, and a similar one perhaps, was, on Sept. 11, 1974, in that North Carolina cornfield.

The pilot's schedule in that crash, in the week before his death, had him getting up at 4:15 in the morning one day to make five flights, 4:45 in the afternoon of the next day for three flights, then 3:30 in the afternoon for four more. The next day he was jumped back to 6:45 in the morning for four hops, followed by a day off, and then rising at 7 a.m. the day before the crash. On the morning of his death, he rose at 3:30 a.m.

According to Dr. Stanley Mohler, former chief aeromedical applications officer for the FAA, such a schedule is plainly dangerous. Mohler used a fatigue index to measure Capt. Reeves' state on the day of the crash. A rating of 1.75 is acceptable, and, at the other end of the scale, 2.3 is dangerous. Reeves was ranked 3.27 on the fatigue index.

Biologists have been studying the internal clock-like cycles in plants and animals for centuries and studying similar cycles in humans for about three decades. They say now that the ordinary view of sleep and fatigue is wrong -- the body does not operate like a battery that runs down and then needs recharging.

It is possible for fatigue to be caused by working long, strenuous hours, but another kind of fatigue is more important physiologically. Its effects are as bad, and in extreme cases may be much worse than the common form of fatigue.

The sleep-wake cycle is one of the most important in the body, and other cycles follow in step with its regular pattern.

Bouncing the body out of its regular sleep-wake regimen, particularly by moving sleep time all over the clock, causes havoc with the many linked chemical and physical rhythms. The result can vary from merely poorer-than-usual alertness, to illness, to severe phychosis.

Elliot Weitzman, an eminent physiologist and sleep researcher at Montefiore Hospital in New York, says, "we have many, many studies showing that if you disturb the sleep-wake cycle, or if you shift it along the clock at the same time losing sleep, then you get bad performance on a whole variety of different measures -- in laboratory and in the real world."

Dozens of tests have been made of people suddenly shifted onto night schedules and the results are uniformly dismal -- train engineers miss warning signals more than twice as often, even double warning signals. Meter readers make far more errors, accidents occur at far higher rates during night shifts.

Both physical and mental performance is worse, and the characteristic mark of this kind of fatigue is perceptual mistakes -- misreading dials, mistaking left for right, jumbling numbers in reading them, and so on.

Among the most recent studies is one by Moore-Ede at Harvard. He has found that how long and soundly you sleep is not determined by how long you were up before sleeping. He has determined that the length and restfulness of sleep are directly linked with what time, in the body's own cycle, one tries to go to sleep. Normally a person wakes up when his temperature has risen halfway up from its nighttime low to its morning peak. Trying to go to sleep around this time results in short, restless sleep, Moore-Ede said. It is this kind of patchy, haphazardly timed sleep which plagues pilots, he said.

Thus, the protest over Eastern Flight 212, Charleston to Charlotte, piloted by a man running on a nine-day week who, according to some scientists and the Air Line Pilots Association, misread his altitude because of fatigue.

Flight 212 is not the only example of a possible link between body time and air crashes.

Another case pilots and scientists suggest may have been caused at least partly by fatigue was the Western Airlines crash at Mexico City on Oct. 31 last year. The crash occurred when the pilot landed on runway 23-left instead of 23-right, for which he was cleared. The jet rammed a cargo truck, and spun into a building, killing 79 people.

The accident occurred at about 5:30 a.m. "That time is the worst time possible time of the day, in the body cycles of most people," said Charles Ehret, a biologist and senior scientist at Argonne National Laboratory. "It is just the time of day you would expect to get this kind of discrimination error, left from right, one number for another, and so on. This case looks suspicious, though we don't yet have the pilot's schedule for the week before the crash to back up the conclusion."

Another crash which appeared suspiciously linked to biological fatigue errors was that of a Pan Am jet in the South Pacific in April 1974. The pilot's schedule had him depart San Francisco at 7:44 p.m. and arrive in Honolulu at 1:32 a.m. The next day at 3:39 a.m., he flew to Sydney, arriving at six in the evening. Next day's duty had him leaving for Jakarta, arriving at 1:30 a.m. That same night at 2:18, he left for Hong Kong, arriving at 6:40 in the morning. When he left Hong Kong at 4 the next morning, he crashed near Bali, having broken not only his body's cycles several times, but also time zones and date lines as well.

Moore-Ede mentioned a couple of more direct evidences of fatigue in near-accidents recorded by the Aviation Safety Institute, which takes confidential reports from pilots on dangerous occurrences.

"One Boeing 707 heading for Los Angeles was seen by controllers shooting over the city at 32,000 feet, heading out west over the Pacific. Apparently the whole crew had fallen asleep, and had to be wakened by warning signals from the tower," Moore-Ede said.

In another case, he said, on a take-off from Honolulu, just as the jet was up from the runway, the copilot noticed his pilot had fallen asleep.

A spokesman for the FAA said that perhaps the chief reason the agency has avoided using the new scientific information in its rulemaking, apart from the fact that the principles are not well understood by FAA staff, is that the agency is afraid that massive changes in scheduling by the airlines might be required if the principles are taken into account. That would be lawsuits and other difficulties the agency would not like to face now.

Scientists, on the other hand, say minimal changes in the computers' scheduling method might be made to take pilot body time into account.

They point out that Britain, Germany, and the Scandinavian countries already take the pilot's body time into account in scheduling their flights. Britain, for example, requires that bumping night sleep and day sleeping against each other must be avoided if possible. The same rules require that pilots have a break of at least 32 hours in every seven-day sequence of flying, and that within those 32 hours, there must be two spans between 10 at night and eight in the morning. This allows pilots to maintain, or quickly return to a regular sleep-wake cycle while flying long sequences.

The british also demand that pilots return for three days in every 14 to their home base, so the pilots can get three good sleeps at home -- in the nighttime.