Three hundred miles off the coast of Bermuda, the sea is sapphire and sparkle, a saucer meeting sky. Waves swell and break in muted roar, and flying fish skim across the whitecaps.

Eagle heads east-northeast through the Atlantic, her sails curved against the clear blue day -- 22 Dacron triangles and squares that layer her three masts like clouds. She makes seven knots, rising and dipping through the eight-foot swells, leaving a trail of foam, looking like a ship that Blackbeard sailed.

On board is a city of people, all in dark blue baseball caps. They climb rope spiderwebs or stand around and talk, leaning at an angle as if drunk. Some mop while others hose, their portable water pumps revving like lawn mowers. They feel the lift and pull and spray that a water skier feels, and the deck vibrates with force.

Eagle had left Washington seven days before, motoring down the Potomac and then setting sail for the ocean, her course the direction of the wind. Her crew numbers 200, most of them Coast Guard Academy cadets, and their cruise is a lesson on the sea. In two weeks they will cover 2,000 miles of mid-Atlantic, going east almost to Bermuda, south as far as Charleston, S.C., and then heading back to the mainland and liberty in Norfolk.

For all that time there will be no sight of land, no television reception, no afternoon beers. After a while, the miles of ocean will look the same, and their minds will numb and the beauty of the ocean will blanch. After a while, they will feel like the world is only Eagle, a sailing ship the length of a football field.

She has masts 14 stories high, four galleys and four levels of deck, two teak helms. On board are electric, metal and woodworking shops, lounges with leatherette couches, a suite with mahogony walls, labyrinthine passageways that smell of detergent. The crew sleeps stacked in triple-decker bunks, 20 men or 20 women to 10-by-15-foot compartments. In the hold are stores for four months: steaks, peanut butter, popcorn, fruit, olives, taco shells and toothpicks with cellophane feathers on the ends.

There are no mail calls on Eagle, and news comes late, if at all. Time is measured by the smell of sizzling bacon, the clang of a brass bell, the silver blast of a boatswain's pipe. Without compass, chart and sextant, the rise and fall of the sun and the moon, Eagle could be anywhere, anytime. "Just over the horizon could be Africa or Europe or Connecticut," says Capt. Martin Moynihan.

Eagle is an island under sail. She makes her own water, turning salt to fresh at a rate of 7,500 gallons a day, makes electricity with a turbocharged generator. She carries an M16 rifle and a couple of .45 caliber pistols, a doctor on loan from a Navy submarine base, and a barber who doubles as chief cook.

Her sails capture 21,500 square feet of wind and are controlled by 170 lines tied to brass pins on teak rails. When the brass is polished, a cadet can see the reflection of a speck of dirt in his eye. Her decks are steel, painted with a gray mixture of epoxy and sand that is good for footing but bad for shoes. She can make 18 knots under sail, and if the wind gives out she can fire up the 1,000-horsepower diesel that the snipes in the smoke hole call Max, and make 11 knots.

Sailing is really physics: The setting of a dynamic airfoil, a sail, in opposition to a static hydrofoil, a boat, in such a way that a desired vector, or course, results. But on Eagle, sailing is an enlisted man named Tramp who carries a picture of Eagle in his wallet, an executive officer who sits high in the ship's rig and reads law books, the captain named Moynihan who wept when the citizens of Cork, Ireland, turned out in hundreds to welcome Eagle to their port, and the chief warrant officer who wants to die on Eagle.

It is the third-class cadet who leans over the rail and stares, breaking silence to say only that the ancient mariners believed that sea foam is made when a mermaid dies, the first-class cadet who once dreamed of "big gigantic spiders" hanging from the masts and gobbling up Eagle's deck crew. It is a cadet who chose the Coast Guard over West Point because she liked blue uniforms better than green, an enlisted man who joined because it was "the least military of all the services," and officers who make pizza on morale night while two dozen of the crew dance a dance called the James Brown to a song called "Drop the Bomb" that blares from a boogie box.

Sailing on Eagle is getting a truck driver's tan, brown from the bicep down, tasting salt water above the lip, climbing the foremast rigging at night to kiss the Coast Guard pennant, then lingering at 147 feet 6 inches to watch a full moon burn a path across the midnight sea. Sailing on Eagle also is being military, following orders, rules and procedures: the book. In this case the book is "Eagle Seamanship," copyright 1979 by the Naval Institute Press in Annapolis.

Eagle is working 20-hour days but learning, as a weightlifter or runner learns, that progress often is measured in pain. Sailing on Eagle is a poem and a metaphor, an insight into nature and an insight into self.

"You know," says First Class Cadet Pete Chittenden, "the weird thing about Eagle is coming home after a cruise. You walk on the street and know that all these people have no idea you were out at sea on Eagle. You can show them pictures, but somehow the pictures never show the feelings I had when I took them. And when you try to explain . . . well, to talk about it is to kind of put it down, if you know what I mean, to make it trivial.

"It's like trying to explain how you feel about life."

Tomorrow: Military life under sail