Next March or April, if all goes as planned, Glenn Tremml will insert himself in a strangely beautiful plastic envelope suspended from hollow wing struts of graphite epoxy, climb atop a sort of reclining bicycle inside and pedal himself 69 miles through the air from the island of Crete to the mainland of Greece.

By so doing he will reenact in part one of western civilization's great and enduring myths -- the legend of Daedalus, who built wings of wax and feathers and, in fleeing imprisonment on Crete, captured the dream of human-powered flight.

"Actually, more people know about his son Icarus, who didn't make it," says Tremml, who was in town the other day to speak to the Smithsonian's Resident Associates. "We decided not to name the plane Icarus."

Tremml's flight is being brought to you by those wonderfully mad scientists at the Massachusetts Institute of Technology -- the same sort who design containers for tossing eggs safely from high buildings, and make lead balloons that fly. They are building the plane. Tremml, a perfectly normal-looking University of Connecticut medical student of 27, is only the pilot. And, of course, the engine.

His looks are deceiving. Beneath the predictably preppy uniform of the Dartmouth grad (oxford cloth shirt, khakis, dirty bucks) lies the author of "Effects of Ascorbic Acid on Prostaglandis Synthesis in Human Lung Tissue"; a surveyor of the interdependency between ant colonies and acacia trees in the Costa Rican jungle; an investigator of bluefish cardiovascular response during studies at Woods Hole Oceanographic Institute; an Eagle Scout expert in judo; a one-time teen-age yacht-racing champion; a competitive diver, windsurfing instructor and show horseman (dressage) who also stars in tango contests.

He even does windows. "To support myself in medical school I work as a housekeeper for a family in West Hartford," he says.

What led him to the cockpit of the world's longest-flying human-powered aircraft, however, is an awesomely efficient physiology. Though his 5-foot-9, 150-pound physique is not obviously imposing, he has turned out to be stronger pound for pound than anyone Daedalus medical researchers have yet discovered.

Last Jan. 22 he pedaled the Michelob Light Eagle, a 92-pound, plastic and piano-wire Daedalus prototype with the wingspan of a DC9, through a two-hour, 13-minute, 37.2-mile flight at Edwards Air Force Base, Calif. The flight eclipsed the history-making distance mark set by Bryan Allen eight years ago when he pedaled the Gossamer Albatross 22 miles across the English Channel.

Moreover, while Allen said only sheer will powered him the last 100 yards, Tremml says mechanical rather than human problems caused the Light Eagle to touch down when it did.

"I had plenty left," he says. "I don't know how much, exactly, but I could have gone much farther."

The capacities of the endurance athlete elude comparison with those of the rest of us. Tremml, for example, competes regularly in triathlons, in which contestants swim a mile, then bicycle 25, then run 6.2. He has never finished below the top 3 percent of finishers in any event. Energywise, his January performance in the Light Eagle was roughly equivalent to running the 26.2 miles of a marathon in less than three hours while simultaneously flying a hang glider. The flight from Crete will equal two sub-three-hour marathons back-to-back. Tremml once ran the New York City Marathon, but says "running is actually my worst sport. If I'm going to push myself like that for three hours, I would rather do more than one thing. Of course on this flight, I won't have that choice. Hopefully."

A competitive swimmer since the age of 12, he appears to view with intrigued detachment the near-bionic aspects of his metabolism, which are enough to put a weekend jock off his Gatorade. Tremml's weight, for example, hasn't varied more than two pounds up or down in 14 years. While the average person off the street waddles along with perhaps 20 percent body fat, and conditioned athletes generally range between 10 and 15 percent, Tremml consistently measures out at 6. And, until recently, he ate whatever he wanted.

"It was a well-balanced diet, I guess, but heavily subsidized with junk food. I never gave much thought to it. Now I try to concentrate more on carbohydrates, and that does seem to make a difference in my performance." For two days before the California flight, he said, "I virtually lived on spaghetti and brownies."

A 2 1/2-hour human-powered flight, he says, is "a lot more difficult than a 2 1/2-hour triathlon. You can't ever back off and get your wind again. The plane needs a minimum amount of power just to fly. As soon as you back off, you start losing altitude."

Plus you're controlling the plane in flight -- no small feat -- and dealing with things that go wrong. On the Light Eagle flight there was a problem with the device that clipped Tremml's right foot to the pedal shaft.

"It kept slipping off the pedal. So I would have a few seconds of pedaling with one leg and trying to get the other clipped on. A minor change the next day corrected that problem, but we didn't run into it until the day of the record flight."

A second problem was water.

"I sweat off about a liter of water an hour pedaling the plane. That's 2.2 pounds. So we had a five-pound bottle of water on board for me to drink. We tested the valve right before I took off, but the valve system failed in flight. So I was sweating off two pounds of water an hour, with nothing to drink. Plus hauling around five pounds of water I couldn't get to.

"Then, toward the end of the flight, the windshield fogged up." The heat he generates in flight, he says, "is about the output of a hair dryer. You can think of turning a hair dryer on inside of a plastic bag and you'll get an idea what the cockpit was like.

"It was a triangular course requiring some maneuvering on the turns. I was trying to conserve energy, keep pedaling, fly the plane efficiently and at the same time try to overcome the pedal problem and try to figure out what to do about the water problem." Afterward, Daedalus Project Manager John S. Langford III "asked me was I ever bored at any time during the flight. That was not a problem."

What was a problem, he says, was the toll muscular exhaustion takes on coordination. "I found in triathlons that after swimming a mile and cycling 25, when you go to put on your running shoes for the running part it's very difficult to tie the laces. Now, any idiot can tie his shoes, but when you're exhausted even a simple task like that becomes very, very difficult." When the pedal problem reappeared the fourth time, Tremml found he couldn't coordinate his legs well enough to get his foot clipped back on while still pedaling. It was that failure that ultimately caused the Light Eagle to touch down, officially ending the flight.

Project Daedalus traces its nonmythological roots to 1979, when an MIT team built an easy-pedaling, 10-mile-an-hour aircraft named Chrysalis to fly across the English Channel. At stake was a prize of 50,000 pounds put up by British industrialist Henry Kremer for the first cross-channel flight under human power. Only seven days after Chrysalis' first airborne test, however, the Gossamer Albatross made its historic flight and Chrysalis was relegated to the status of a sport aircraft.

The MIT team went on to build a smaller aircraft called Monarch, which in 1984 set a world speed record for human-powered flight, negotiating a diamond-shaped 1,500-meter course at 21 miles an hour. Or, as project director Langford puckishly describes it, "mach .03."

Langford, a former aeronautical engineer with Lockheed who looks a bit like a cerebral John Denver, personifies the restless, mischievous minds of MIT. The holder of master's degrees in aeronautics and astronautics and in defense policy and arms control, and a doctoral candidate in aeronautics and public policy at MIT, he is currently a research staff member at the Institute for Defense Analyses in Alexandria.

After building the Monarch, he remembers, "we were looking around for something to do next ... something that would drive the technology" of man-powered flight. Duplicating Daedalus "seemed like a natural."

The flight from Crete, however, would be more than triple the distance of the Gossamer Albatross flight and none of the other man-powered aircraft "had flown longer than five minutes. We didn't really know if it was possible."

So with $74,000 provided jointly by the Smithsonian's Air and Space Museum and MIT, the team spent from April 1985 through April 1986 researching everything from high-tech aerodynamics to the meteorology of the Aegean to see if the project was even feasible. They concluded it was. But just barely.

"One of the crucial unknowns was physiology," Langford says. "The Army and others have done research on what the human body is capable of doing in spurts, but believe it or not, there has been very little real medical research on endurance physiology. We didn't know if anyone could pedal that hard for that long with the efficiency we needed. We did a literature search and the one name that kept popping out was Professor Ethan Nadel at Yale. So we asked him to come talk to the team at MIT and, as has happened with others, he was captivated with the project and now is our principal investigator in physiology."

Tremml, meanwhile, knew nothing of the Daedalus project. But by chance he was working as a research assistant at a medical research institute in New Haven, downstairs from Nadel's laboratory.

"I would go running at lunch with some guys who worked upstairs and they would tell me about all these famous athletes they were testing in the lab -- people like John Howard, the fastest man alive on a bicycle ... so I went up to peek in and get a look at them."

When he learned about the project and the team's search for a human engine, "I became very interested in them. But they weren't interested in me because I wasn't a national-caliber athlete. Then Dr. Nadel found out I was a licensed small-plane pilot -- which most of the other athletes weren't -- and he granted me my audition."

The Daedalus people tested him on a slowed-down flight simulator originally designed for jet pilots. They weighed him and measured him and tested his body fat. Finally they strapped him in a stationary cycle "ergometer" in the basement and had him pedal for four hours at power settings 10 percent higher than they thought the flight would ever need.

While a lot of athletes could pump for more power than Tremml, he says, he produced more power per unit of body weight -- "which is much more important in a plane than on a bicycle."

Finally they decided he should make the key January test flight in the Light Eagle. Until they found Tremml, the top pound-for-pound pilot was Lois McCallin of Belmont, Mass., another triathlete. Now they're looking for two more.

"I had to be better than Lois. Anybody from now on will have to be better than I am," Tremml says. "Or, to put it another way, I'm the worst they'll take."

Tremml grew up in Milford, Conn., the only child of two schoolteachers who encouraged him to pursue -- and test himself against -- his myriad interests. Athletics were always a part of his life, but far from the only part. Both before and after his undergraduate years at Dartmouth (B.S. in biology, 1982) he threw himself into a succession of activities ranging from ecology surveys in the Costa Rican jungle to ballroom dancing, generally moving on after a couple of years to something new. With a full schedule in medical school plus a full-time job, Tremml was not exactly idle even before the Daedalus project. Now he is approaching some sort of twilight zone of organization, endurance, concentration and discipline.

Every day he gets up at 6 a.m. and swims a mile. Then he eats breakfast and goes to class. When he gets out of the lab in the afternoon he either runs nine miles or cycles 40. "When I get back if there's a half-hour or so before dinner I am mowing the yard or cleaning the bathrooms or doing something else for the family I work for. It's a big house -- four stories. Then I study until 11.

"The psychological aspects are the hardest," he says. "It is always harder getting up and getting to the pool than it is to swim; harder to make myself go to the library than it is to study."

December, he says, was the worst. He was in the middle of exams. His friends were home in Milford, the project was in Boston, and he was in West Hartford. He rarely spent time with anyone else. Even the family he worked for was at work when he got back from swimming and in bed when he got back from school. And the short winter days were cold and dark.

"I remember one particular evening, I had gotten out of lab late. The weather was just on the freezing mark and I wasn't sure I could cycle my 40 miles before dark. But I went. And I was at the exact farthest point away from home on an isolated road near Burlington when I got a flat tire. And I changed it. And the spare tube was flat. So I got out the repair kit, which I had never opened. And the tube of glue inside, which was still sealed, had no glue in it.

"So there I was, soaked with sweat, which was now freezing. It was getting dark and I'm at least a mile from the nearest house. And I decided that if I didn't die right there on the road I would at least quit the project."

But instead, balancing his bike on its one good tire, he walked it through the biting cold to the nearest house "where there turned out to be a kid who had worked in a bike shop and had several repair kits. And he helped me fix the tire. And I pumped it up. But then I still had 15 miles to pedal home. Through below-freezing weather. In the dark."

Tremml slumps silently for a moment at the memory. "At times like that," he says finally, "I just wonder what I'm doing."

Solitude comes with the territory. "There's no question there's a social cost," he says. Even if he had time for romance, "no one else in the world has a schedule like mine." Last summer, he says, "was a blur." But he has managed to form "small compatible alliances." Sundays he goes home to Milford to see his parents; on noncycling days, he runs with two or three people who run at his pace. Occasionally he pedals with a cycling club. "It's helpful to have some others pushing you along," he says.

"I keep very detailed records of how I train every day. When my times start getting slower, or I just feel tired all the time, then I take a day off." And no, it's not a totally joyless life. "I've been known to have a beer," Tremml says.

The feasibility study was the first phase, the prototype flight (a $195,000 effort underwritten by Anheuser-Busch) was Phase 2. Project Daedalus is now in its final ($830,000) phase and looking for sponsors. The actual Daedalus plane is being built. The team has found a way to shave 20 pounds from its prototype design, in part by utilizing some pink Styrofoam that is already troubling Langford's esthetic sense. The next flight will be in August: an overwater practice run of about 10 miles from the old Charlestown Navy Yard in Rhode Island out to Block Island. There has been no wind tunnel testing. It's all done these days with computers. And with some 20,000 volunteer man-hours involved in construction of the Daedalus, Tremml says, with a smile, team members have assured him "that any crash will be fatal."

The Daedalus team, which once numbered only four or five, has grown to 21 full-time people plus another 15 part-timers. Tremml is probably no more intense about the project than its other members, some of whom have spent endless nights wrapping carbon fibers in epoxy around poles to form the strong but feather-light hollow struts that will frame the Daedalus wings. "It's a very focused group," says Langford. "We've had to enforce time off." It includes such esoteric helpers as Nilton Reno, a Brazilian student doing graduate research in dynamic meteorology (the Daedalus weatherman) and Sarah P. Morris, a classics professor at Yale who has researched the origins of the Daedalus myth.

Actually, it turns out, there were several versions of the legend, some of which have Daedalus landing as far away as Sicily, roughly 300 miles from Crete. "But the Greeks were island hoppers," says Langford. "The first step would have been ours -- to the mainland."

On the appointed day next spring, the team will start early, possibly even at night. "The Icarus part is right," says Tremml. "It's the heat that can kill you on this flight."

Fueled by high-tech drinks that include something called glucose polymers, a thin beverage made of long strings of sugar molecules linked together in such a way as to fool the stomach into speeding them into the bloodstream, Tremml will pedal off the beach of Crete, heading northward over calm seas. It will have to be calm, Langford says: Headwinds almost aborted Allen's flight across the channel.

The plane's designed speed of 15 mph is a carefully constructed compromise: Faster would tax Tremml too much; slower would leave him exposed too long to the mercurial Mediterranean weather.

Keeping the 11-foot, 1.9-pound propeller of Kevlar-wrapped Styrofoam rotating at cruising speed, Tremml says, takes 70 percent of his aerobic capacity. Getting the plane off the ground takes 140 percent, "sort of like a quarter-mile sprint before the marathon."

But once into the air and underway, he says, manpowered flight is "almost completely silent. The loudest sound is the sound of my own breathing."