ABOARD HURRICANE HUNTER FLIGHT 43-- It was 5:30 a.m. on a sunless dawn when Dave Turner announced it was time for "a coffee break" and banked his lurching computer-packed research plane out of the vortex of 170-mile-an-hour winds and into the relative calm of Hurricane David's outer rim.

Sweating, greenish faces throughout the plane managed weak smiles. The specially strengthened four-engine turboprop had just finished the first of the day's three stomach-churning trips through David, a 10-mile-high, 300-mile-wide hurricane scientists rank among a historic handful of major league killer storms.

Hours earlier, it had killed at least 20 persons and left some 60,000 homeless on the Caribbean island of Dominica. Now it was whirling westward past Puerto Rico on a course no one could alter or predict.

Strapped in behind Turner in the cockpit sat Dr. Robert Sheets, a boyish-looking, 42-year-old meteorologist, reading computer video screens as they analyzed the heart and soul of the storm.

Outside, the gales had diminished to a mere 60 knots that wrenched the plane into only occasional 100-foot plunges.

"This is one of the three or four roughest storms we've flown through," remarked Sheets, a 250 flight veteran known to his staff as "Mr. Hurricane" who heads a special hurricane research group of the National Oceanic and Atmosphere Administration (NOAA).

He and his highly trained, welltanned teammates earn their federal paychecks chasing leviathans of weather in odd corners of the globe and harpooning them with puny human technology.

It is not a calling for the faint of heart.

Once in 1971 Hurricane Edith sent their plane -- an older and less powerful model -- spinning "dumped out of control," Turner remembers.

He fought for control and won, but they turned back, leaving Edith temporarily unanalyzed.

"We were just all scared -- -- less," remembers another technician on that flight.

Still, the flying researchers yearn for the scientific revelations a major hurricane offers and David, a rare monster, had their blood up going in.

The plane had taken off at 3 a.m. from San Juan, where the winds heralding David's approach were already bowing the palm trees.

Their modified Lockheed Electra was crammed with $4 million worth of state-of-the-art instruments designed to steal hurricane secrets and those of the weather itself.

They included nose and belly radar, cameras, computers, laser probes to study cloud physics, tubes for launching ocean-sensing canisters and a satellite linkup to the NOAA Hurricane Center in Miami.

A spokesman for NOAA said the plane costs $1,500 an hour to fly.

The hurricane hunters' primary mission was to fix a storm's size, location and speed, and to relay the information to Miami for planning evacuations and the like.

But they also search for meteorological knowledge that will save lives and property with improved forecasting and, ultimately perhaps, permit "beneficial modification" of hurricanes themselves.

At about 4:15 a.m., approaching David's spiraling outer rain bands, the plane began its descent to 1,500 feet. Fifteen minutes later, 20 miles from the eye, the winds were shrieking at 100 knots. The plane began to slam up and down and side to side like a model T in a gully. Sheets of lightning slashed the towering dark clouds outside.

As the eye loomed larger on the radar screens, the jolts slammed the passengers up against their seat straps, then down again, over and over and over.

Heavy spring-mounted instrument consoles lurched in a mad disco dance, nearly crushing the foot of metorologist Jeff Hawkins.

Suddenly the barometer plunged, the jolting stopped and the plane was caught in a eerie sunlit stillness.

Outside a translucent white column of sculptured clouds, tiered like the galleries of some enormous phantom opera house, encircled the plane.

We were in the eye of Hurricane David.

Fifteen hundred feet below, the green Caribbean heaved with huge, foam-streaked seas. Above shone a tiny circle of blue sky.

Abruptly the plane plunged again into the storm. uring each pass, the navigator crossed through the storm while the Tom Bergner could be heard over the headphones, repeatedly telling Turner and the other pilot,Bill Noble, how to adjust the plane's heading so that it would angle into the wind safely: "227, right drift 40 degrees . . . I guess we're in the ball park . . . "Okay, this is the rough wall" . . . "Winds 395 (degrees) at 110 with a 40-degree drift . . . Heading 250 when convenient . . . "

"The hairiest part is fighting to control the plane through the eye wall, where the winds reach their peak intensity in that spinning "chimney," explained Turner, who has been flying hurricanes for 15 years.

"you don't want to get caught with the wind on your tail in the eye wall," he said. "You crab maybe 40 degrees, and you try to cut the wall at a right angle, keep the wind off your beam. That's the trick. If you get caught in the eye wall, the wind could whip you around and -- " he shrugged, "do you in."

For five hours the plane criss-crossed through the storm while the scientists fought to keep their instruments registering and their dinners down.

They have their own scale for classifying storms a scale keyed to the exclamations of flight engineer Alex Ricci, "We go by how many times he says 'Jesus Christ!' and how high his voice gets," said one of his coworkers.

"I said it 18,000 times today, I'll tell you that," Ricci said after his encounter with David, "If they were all like this one, I'd quit."

The research team, scientists and pilots alike have plenty of stories, over a beer in one of the airport hotels where they spend much of their year.

They also talk about their families back in Miami, where they all live, about Little League and softball with the kids, and about how many wedding anniversaries and Christmases they've missed because they were studying air currents off Diego Garcia or measuring typhoons in the Indian Ocean, or "assessing the environment" in Alaska.

"We love our work. We're proud of what we do. This is a pretty tough bunch," said NOAA meteorologist Jim McFadden. "But the older I get, the scarier it gets. Like driving in traffic or anything else, you start thinking how maybe your number is coming up."

Some like Sheets, see the flying as a necessary evil. "I don't get my kicks by doing this," he said during the flight through David. "It's the data I'm after. But you do get to see some spectacular seas."

Hurricane hunters don't usually die in action, but one who did at least figuratively was William Friedman, a veteran NOAA research pilot who succumbed to a heart attack nearly a year ago.

During the last pass through Hurricane David his friends carried out one and they don't mind sharing them last, long-remembered request. They scattered his ashes through a bathythermograph launch tube in the eye of the storm.

"This job is good for 30 minutes of conversation anywhere," grinned bachelor radar man W. Peter Wirfell, 24, refusing a Dramamine. "We had our hurricane filed program books out on the [commercial] flight coming down, and the stewardesses all seemed very impressed."

Later, however, Wirfell was somewhat sobered, admitting that he like several other crew members, had come close to needing a motion sickness bag for the first time in his life.

"It was only my pride that kept everything down," he said. "That was a hell of a pass."

As federal employes, however, the scientists say the worst pass of all was the one a civil service job classifier took a few years ago when he flew with the scientists to gauge the demands of their job.

The classifier flew through Hurricane Ginger, which turned out to be a very mild storm, and downgraded them from GS 14s to GS 13s. McFadden explained. "If he had flown through Edith, they might be GS 15s today."

Or through David.

As the plane turned and climbed away from the storm, several men gathered at a bubble window to remark on the clarity of the 300-mile shield of cumulus clouds, the hurricane's "hat" that curved clear and white against the blue Caribbean sky.

Some of the scientists, including Sheets, had not slept for a day and a half. But they might be back in the air, flying another mission, in as little as 10 or 15 hours.

The word came from Miami. Out in the Atlantic, and over in the Gulf, two more storms were gathering force.