ON ONE OF THOSE windless mornings when the Florida seas lay as flat as glass, a sun-bronzed former chicken farmer named Mel Fisher dove into 20 feet of water off Key West and began sifting the sugar-white sands on the ocean floor.

Above him, the unmuffled engines of a converted tugboat groaned, aiming a strong draft of water downward to stir clouds of silt. This was the exact spot where the boat's magnetometer had located yet another metallic anomaly.

There had been seven false alarms on this hot spring day in 1971. The first was a spent Navy torpedo, the second on old Air Force bomb. Then came readings from four steel fishtraps, a 50-gallon oil drum and, curiously, a baby carriage. But no sunken treasure.

"Then we came to this spot that looked like the Sahara Desert, all sand." Fihser recalled. "I found one lead ball, about the size of a marble. I came up right away and said, 'This is it!'"

The musket ball was free of rust and barnacles, as clean as if it had dropped into the ocean only days earlier. But its discovery meant that a 47-year-old dreamer had found a wreck . . . which treasure salvors had been hunting for three centuries, a grande dame of a Spanish galleon called the Neustra Senora de Atocha. She had foundered off the Marquesas Islands during a hurricane in 1622, and had gone down carrying 300 Spaniards and one of the most spectacular cargos in maritime history - 47 tons of silver and gold.

Although he knew there was a fortune to be retrieved, Fisher could not have known what his quest would cost him over the next seven years: nearly $5 million, an SEC investigation, accusations of fraud, a bitter fight with two greedy governments and four lives, including his eldest son's,

Today he is a triumphant man, no less obsessed but certainly vindicated. No longer does anyone dispute that Mel Fisher has found the fabulous Atocha. And, in recent weeks, a federal judge in Miami has decided that the treasure belongs to Mel Fisher, and that the state of Florida and the United States government better pack up their snorkels and go away.

So far the salvage operation over the scattered wreck has yielded a priceless astrolabe, a golden chalice, jeweled drinking cups, a golden dragon, nine cannon and hundreds of gold and silver coins - an $18 million trove, but merely a fraction of what the 600-ton galleon carried when she left Havana on the afternoon of Sept. 5, 1622 with 901 sivler bars, 300,000 coins, 15 tons of copper and an untold fortune in jewelry and artifacts.

"After I found the lead ball, everybody thought we were going to find pieces of treasure all around. It wasn't like that," Fisher said. "There was nothing else."

The tug Virgalona chugged on slowly. It would cover 120,000 linear miles before Fisher's underwater archeological team would begin rigging surface buoys and nylon subsurface grids to mark the Atocha site. Each sector measure 25 square meters and required its own comprehensive search.

Sunken treasure does not, as the movies would have us believe, glisten seductively from the sandy ocean floor. "It's spread out of miles," Fisher said. "Acres and acres of sand had to be removed."

In the Atocha case, much of the fortune lay below 12 feet and three centuries of silt. Reaching it required the use of Fisher's unique "hole-dusting" device which uses the backwash from the boat's propellers to dig small craters in the ocean.

The sands of each crater are searched inch by inch. If the boat's engines should suddenly cut off, the divers must scramble out of the crater before it caves in on them. More than once, Fisher has been forced to use the hole-duster to free one of his own salvors.

Whenever an object is spotted, it is approached gingerly. It could be nothing more than an encrusted conch shell, or as priceless as an 18th-century gold necklace. Nothing shimmers after 300 years in salt water. "All you see is a piece of something sticking out, and the first impulse is to grab it. You don't know what's on the other end," Dolores Fisher said. "But you have to wait for the dust to clear because you want to make sure that it comes out intact."

A few days after Fisher found the musket ball, a single dime-sized coin was brought up and the crew celebrated. But weeks passed before diver Don Kincaid burst to the surface clutching a braided eight-foot chain forged of solid gold. Fisher's wife, Dolores, clapped and danced on the sun-bleached deck. Fisher himself, a husky 6 feet 4, broke into tears. By the end of 1971, the crews of Fishers' three salvage tugs had brought up an encrusted anchor, an olive jar, and 19 gold coins "stacked like poker chips."

But were they from the Atocha? Fisher wasn't really sure. Some of his crew members believed they were actually working a smaller galleon, La Margarita, that splintered over the shoals in the same 1622 storm. The Atocha was still a whispered hope, Fisher wasn't interested in any other wreck.

"I'm not going to be sidetracked. I'm going after the Big A," he promised his divers. Says Dolores Fisher. "It was a long time before we had proof. There was doubt in all our minds."

Sunken treasure had been on Fisher's mind since the day a classmate loaned him a Robert Louis Stevenson novel in elementary school. When he was 11 he built his first diving helmet out of a five-gallon paint can, slicing up one of his bicycle tires for a rubber collar and melting down his lead soldiers for ballast. To try it out, Fisher jumped into a rock pit while a friend used a bicycle pump to send him air; the young diver came up sputtering.

He later went to Purdue University to study engineering, and joined the Army Corps after World War II. After a brief career in the construction business, Fisher found himself tending chickens on a huge California farm. "Those darned chickens laid 10,000 eggs a day," he recalls sourly. "They never stopped."

In the late 1950s Fisher opened one of the country's first SCUBA shops, and this soon led to a weekly television diving series based in California. Business boomed, and after teaching 65,000 swimmers how to breathe underwater, Mel Fisher says he was ready to retire and do something he really wanted: hunt for lost treasure.

He joined with a group of salvors working an intriguing wreck off St. Lucie County on Florida's upper east coast. Using the "hole-ducter" the divers discovered several sunken galleons, and recovered more than $2 million worth of gold, jewelry and artifacts.

The discovery of the so-called "1715 fleet" off St. Lucie was the beginning of Mel Fisher's reputation, and it's not as pristine as the waters he plumbs. At its best, treasure hunting is a shoe-string operation where multi-million dollar figures are bandied about recklessly. It requires patience, well-heeled investors and astute bookkeeping, not to mention rugged divers and keen architists.

"Mel has been described quite aptly as the best and worst of all of us," says a rival treasure hunter, one of three dozen seriously working Florida's coalstal waters.

Fisher wanted the Atocha in a big way, and in fact spent 101 days searching for it in 1968 - at the wrong islands. To raise money, he sold off shares of his dream at $12,500 a shot to investors who were promised one-quarter of 1 percent more than $1 million for his company before the SEC stepped in in 1973 and said he was selling unregistered securities. Fisher stopped.

From the outset, his competitors challenged the legitimacy of the Atocha find. Several coin collectors said Fisher was peddling phony Spanish coins to lure investors to his Treasure Salvors, Inc. Fisher denied it and carried his Atocha coins all around the country to convince skeptics.

One of his most persistent critics was Burt Webber, a Pennsylvania based treasure hunter who had a copy of the Atocha's manifest. When Fisher displayed three silver bars he claimed came from the Atocha's hold, Webber, said he was full of baloney.

Today Webber admits Fisher has not been hawking fool's gold. "I acknowledge the fact they've found debris positively identifying the wreck as the Atocha," he says. "It's also quite obvious they haven't found the nuclei, the main ballast."

And Webber criticizez Fisher, saying he spends more time drumming up business than bringing up artifacts. "There's no excuse for going seven years without finishing it off."

But another of Fisher's competitors, Jack Haskins of Islamorada, Fla., says, "They've done a very careful job, no doubt about it. He beat us to it, and that's the name of the game. When one guy finds it, we congratulate him - and curse him in the dark."

But Mel Fisher didn't need a curse, and it was not fickle tides and currents that threatened his hold on the Atocha. As the vaults of Key West banks filled with Spanish treasure, the state of Florida and U.S. government each demanded a share. Fisher was of no mind to argue. "I offered to donate some, millions of dollars worth," he says today.

"It was never the money. It was the hunt, the challenge. Some guys go to Siberia for polar bears," he says with a shrug.

So when he brought up a wheelbarrow full of gold coins and dumped them on the desk of an astonished Vero Beach bank president, Fisher assiduously set 25 percent aside for the state of Florida. And when he brought up a musket, a gold chalice and a five-karat emerald, he dutifully handed them over to Florida state agents, not dreaming he would never use those artifacts agains.

Meanwhile the controversy about the authenticity of the Atocha was stilled forever in July 1975. Fisher's oldest son Dirk, 21, was diving under the Virgalona when he uncovered a bronze cannong measuring 11 feet and weighing 3,600 pounds. Eight more were raised, each worth about $20,000 - and each indisputably marked as part of the Atoch's armaments.

One week after this triumph, Fisher's Atocha operation was in shambles. On July 20, the 60-foot salvage ship Northwind capsized and sank at its overnight anchorage near the wreck site. It happened in the pitch blackness with terrifying swiftness when a fuel valve malfunctioned and 3,000 gallons of diesel fuel suddenly shifted in the hull. The Northwind flipped belly-up, trapping Dirk Fisher, his wife, Angel, and diver Rick Gage in their quarters.

At sunrise, the Northwind's sister ship bobbed alone at anchor. Crew members sighted an orange life raft in the distance, but only seven survivors. The treasure hunters found Dirk's body near his bunk, where he had struck his head and lost consciousness. Angel's body, clad in a hseer night-gown, floated eerily near the stairs where she had huddled for safety as the tug filled.

That afternoon Mel Fisher stood on the Key West docks and sobbed as his divers unloaded the three bodies. It was the second tragedy for the Atocha salvors, in 1974 the 11-year-old son of a National Geographic photographer was killed when he tumbled into the props of one of the salvage ships.

Within days after Dirk's death, Fisher was back working the Atocha more feverishly than ever. So were his other three children. "I felt in my heart Dirk wanted me to continue, to bring in the rest of the treasure. That's why I'm still working on it," Fisher says.

The more he brought up, the more the State of Florida and the U.S. government wanted. By 1977, the basement of the state archives building in Tallahassee was littered with more than 3,000 Atocha items worth more than $2.3 million, worth, according to one veteran treasure hunter, "whatever you can get for them."

Last month, after ordering the U.S. government to leave Mel Fisher alone, U.S. District Judge William Mehrtens agreed with Fisher, who said, "The State of Florida has no business in the treasure-hunting business." In a scathing decision. Mehrtens scolded state and federal officials for letting Mel Fisher do their work for them, then moving in to claim the goods. The judge did everything but call them brigands, which is what Fisher likened them to.

Then Mehrtens ordered the state to give Mel Fisher his $2.3 million worth of treasure back. The state is appealing, and in the meantime testimony given Sept. 8 indicates that $100,000 worth of Atocha artifacts are missing from the state archives building. Mehrtens were enraged, and embarrassed state officials promised to find out what happened to the priceless gold chalice, 523 coins and five-karat emerald that survived so many decades on the ocean floor but not three years in a bureaucrat's basement.

"I don't care if I ever get them back, I really don't," Fisher sighs. "The important thing is that we beat the State of Florida. I let my heart pour out at that trial. They were insinuating we were pirates, destroying artifacts when in fact the opposite was true."

Among tropical treasure hunters there is an unwritten code that they will not pilfer each other's discoveries, no matter how successful the first find or how envious the competitors.

One of Fisher's rivals in the treasure-hunting business says, "To say we're interested only in gold in ridiculous. This isn't the way to make money. We do it for the history, for the romance. I don't know any rich treasure-hunters. Did you ever see where Mel lives?"

Fisher has not realized a nickel's profit from the most dramatic treasure find in Florida's history. The State of Florida and the U.S. governemnt have, until recently, tied up the Atocha's treasure so completely that Fisher says he has not been able to sell any of it for himself or for his 90 investors.

He lives in an old houseboat with his wife. He drives a 1969 Mercury. And while his salary as president of Treasure Salvors, Inc., is listed at $22,000, Fisher says that he has never been paid that much. The payroll for his 15 divers exceed $180,000 a year. He spends thousands more on fuel and - of late - on legal fees.

Private investors and the sale of previously recovered treasure have financed the Atocha search and, Fisher says, "I've never had enough left over for me."

When he's not scouting up new investors and borrowing money to keep his fleet's diesel tanks full, Fisher spends these hot hazy Florida days aboard the 187-foot converted Coast Guard buoytender Arbutus, anchored possessively over the Atocha's grave.

He dreams these days of a tourist exhibit "bigger and better than King Tut" to show off one of the world's richest treasure finds. He takes from the Atocha what it will give him - just days ago his crew discovered a chess piece, a silver bishop forged 360 years ago in Spain - and he hopes each day will bring him closer to the ballast, the mother lode where an estimated $300 million in riches lies buried under 12 feet of Florida silt. "I figure a year and a half," Fisher says optimistically.

Only when it is absolutely necessary does the tanned 54-year-old chain-smoker shed his SCUBA gear, put on some civilized clothes and fly to Miami for one of the countless court hearings that have kept him away from the Atocha in recent months. "I'd rather be diving," he grumbled to his lawyer last week.

But Fisher's presence paid off. The U.S. District judge ordered the State of Florida to post a $1.5-million bond to protect what's left of Fisher's treasure. Mel Fisher stood before the bench beaming, looking for all the world as if he'd just picked a priceless gem from the sea. Hanging from his neck was a genuine gold doubloon. CAPTION: Picture 1, The Southwind, a former Mississippi tugboat, by David Doubllet; Copyright (c) National Geographic Society; Picture 2, trials a plume of sand as she blows craters in the seafloor in the area where the salrors have discovered metal; Picture 3, Melvin Fisher, the treasure hunter's treasure hunter, items recovered from the Atocha to dated include a priceless astrolabe, AP; Picture 4, a gold bar, by Gordon W. Gahan; Copyright (c) National Geographic; Picture 5, no-caption; Picture 6, Fisher, third from right and his wife, Dolores, watch as part of their treasure is divided with officials from the state of Florida in 1975, By Gordon W. Gahan; Copyright (c) National Geographic Society