Jacques Cousteau slips easily into his captain's chair amid brass knobs and crackling radios in the wheelhouse. "Alors, petit diable!" he says to his 13-year-old granddaughter, Celine, whose flashing blue eyes and mischievous grin are not unlike his own, and who is poking a pencil at her brother, Fabian. At 17, Fabian is a sea diver who says he may someday carry on the Cousteau legend. Now he is busy tracking on radar the myriad ships, including a spouting fireboat, that are escorting Calypso toward Washington to celebrate his grandfather's 75th birthday.

Welcome to the Noisy World of Jacques Cousteau.

The great old man, clean-cut in a sea-blue leisure suit, his elbows resting easily on mahogany and brass, gazes out the window with an air of utter calm at the whirlwind of activity. On the foredeck his son, Jean-Michel, 47, a rugged, bearded man who now heads most of the Cousteau Society operations, is doing a standup for a Turner Broadcasting System crew. Calypso's little helicopter, Phoenix, is buzzing around with another Turner crew. The Wilson Bridge drawbridge goes up, and as traffic stops hundreds of people pile out of their cars and line the rails to watch the armada pass.

A paddle-wheeler, the First Lady, is steaming alongside and listing sharply because all the tourists aboard have crowded the port rail to see Calypso. The tourists are singing "Happy Birthday," but someone gets on the radio and tries to stop it because it is interfering with the Turner filming. Celine grabs her grandfather's hand and exclaims, "Ils chantent, ils chantent!" Cousteau seems amused. "For safety reasons," he says, "I am forbidden to show my face , because if I do, that boat will capsize."

Really? He laughs. A Gallic shrug. His famous smile, perhaps the warmest in the world. The deep tan and pure white hair. That nose!

Cousteau at 75, called "Zheek" by close friends, seems as vigorous as ever. Stoop-shouldered but lithe and strong, he strides around Calypso, his famous exploration boat, like a young man. Just two days earlier, the great explorer and oceanographer, author of "The Silent World," the man who mesmerized hundreds of millions of television viewers with "The Undersea World of Jacques Cousteau" and other series, the man who invented the Aqua-lung in 1943 and received a Medal of Freedom from President Reagan last month, was diving with his son to a 17th-century shipwreck off Bermuda.

Last night, cable-TV mogul Ted Turner threw a birthday bash for Cousteau at Mount Vernon. The host was singer John Denver and TBS crews filmed the event, as they did Calypso's sail up the Potomac and Cousteau's participation with Mayor Marion Barry in the weekend's "Riverfest" celebration of a cleaner Potomac, for inclusion in a two-hour special, "Jacques Cousteau: The First 75 Years," which will be broadcast June 23.

In a passionate speech before 2,000 at last night's celebration, Cousteau declared that he will dedicate himself to the "utopian project" of promoting world peace. "I would like to see 1 percent of the military budgets dedicated to a vast and obligatory exchange of children," he said. "Imagine a world where all the children from 7 to 8 have to spend a year on the other side of the fence . . . It would be a formidable barrier against war."

Aboard Calypso on Saturday's run up the Potomac, Simone, Cousteau's wife of nearly half a century, herself a diver who virtually lives on the ship and who perhaps has more sea time than any other woman, remains in her cabin, avoiding the press and hoopla. Later, approached by a reporter as she is preparing lunch in the wardroom, she says only that the weather is unexpectedly "cold. Incredible!" Then with an emphatic, "Ah, alors!" she ducks out a side door.

As for the old man of the sea himself, he says he certainly doesn't feel old.

"I don't see why the figure 75 would be magic," he says. "I just carry on. I don't see any difference. It shows I've been at sea for 55 years of my life. Very few human beings can say that."

In fact, with Turner's backing, Cousteau is now undertaking what he calls the boldest adventure of his life -- a five-year, $15 million circumnavigation of the globe by both Calypso and Cousteau's new experimental "wind ship," the Alcyone, which is partially powered by two vertical "Turbo-sails."

"I intend to live these five years very intensely," he says. "It will be more difficult than any other expedition because of the two ships and flying from one to the other in different parts of the world."

Cousteau says he will produce 20 hours of television for TBS from the trip, which he has tentatively titled "The Rediscovery of the World."

It is interesting that, for the man who introduced generations to the silences and wonders of the deep, life at 75 has become a bit hectic. Friday night, although Calypso was docked just a few miles south at Indian Head, Cousteau stayed at a Holiday Inn in Alexandria. He and Jean-Michel had arrived on the shuttle from New York, having just flown there from Bermuda, where Alcyone has paused for a few days, itself en route to New York for a big publicity blitz. The Cousteaus had been traveling across the Atlantic on the wind ship.

Earlier, Alcyone stopped in the Azores long enough for Cousteau to jet to Washington for his Freedom Medal and return.

Today, as Calypso heads back to its berth in Norfolk, Cousteau heads to New York for a round of media and other interviews. On Tuesday morning, the 11th -- his actual birth date -- he is to appear on "Good Morning America."

Then back to Bermuda.

The chance to dive with his son the other day, he says, "made a big difference. It was a very rare opportunity."

But all of this is simply the price he pays for the magnificent life he leads. Cousteau is a man who always said he didn't want monetary success, yet he has achieved success of another kind, beyond the wildest dreams of most. He is in possession of his soul, and he has not only lived in the natural world but re-created it on film -- cinematography is almost as old an interest as diving -- as a wonderful world of the imagination.

"I'm not a social being," he says, fidgeting during an interview in the wardroom. "By nature I am not attracted by social meetings or shindigs, but I can take them."

Then he pauses, smiling so warmly that it seems to brighten the room. He says, "When we are at sea, we are free."

Pause, smile, fidget.

The "formal" interview in the wardroom, which was to have been an hour, lasts about 10 minutes before Cousteau, unable to contain himself any longer, virtually bolts for the wheelhouse, where he can settle into his captain's chair, keep an eye on things and banter with his family and crew.

During the brief wardroom interview, Cousteau sits at the dining table where everybody eats; there are no distinctions between crew and officers. Cousteau says the five-year Turner deal will be worth at least $15 million plus an adjustment for inflation. Calypso will tour the Caribbean, where Cousteau will dive with Cuban leader Fidel Castro, then head for the Pacific -- New Zealand, Australia, New Guinea, the coast of China -- islands in the Indian Ocean, "and Africa by the Cape. The Congo River, and back to France."

He pauses thoughtfully. By then, he will be 80 years old.

The wind ship Alcyone will take another route, he says, as it undergoes further feasibility tests. Cousteau says he already knows that the idea works and will probably save 25 to 35 percent on fuel bills for shippers who implement it.

Alcyone, he says, is "a beautiful legend from the Greeks," a love story about an "ideal couple." When the man drowns, the woman also drowns herself to be with him, but the gods take pity on such a love and turn them both into birds.

On one subject, Cousteau has usually been silent -- the death of his son Philippe, until then the heir apparent to the Cousteau legend, in a 1979 crash of Calypso's seaplane.

But during his speech at last night's party, Cousteau broke down sobbing as he mentioned "the great absence tonight -- Philippe." Philippe's children, Alexandra and "little Philippe," also broke down crying and went over to their grandfather for comforting after his speech.

Cousteau introduced all four grandchildren during his speech, telling Fabian that he should "be prepared" to take over the Cousteau dream someday and saying that Celine, too, might play that role. He drew applause when he said to Celine, whose hair is cut shorter on one side, "Maybe when you have cut your hair properly, you will remember that a girl is just as good as a boy!"

Aboard Calypso Saturday, Cousteau says that Jean-Michel is his "best friend," and it seems clear that this son, a former architect who began actively helping his father after his brother's death, is devoting his life to carrying on the Cousteau dream.

Cousteau has become increasingly concerned in recent years by the potential destruction of the earth's oceans and rivers. "What is ecology? Is it to protect the whales? Yes, but the main goal is the happiness of people. People will have a better life not on concrete and asphalt. We want to develop and implement as far as we can the necessary ingredients for human ecology. We don't want to go back to candles and horseback, but we don't want to destroy the planet. So every time there is a project we don't like, we try to develop a counterproposal."

Which gets him to the subject of nuclear war and the Soviets.

"Why protect the trees and whales if the world is to be reduced to ashes by nuclear war? So working for an understanding among people is part of our program. This is why I have an American and Russian journalist aboard Alcyone, so we are trying to contribute a little bit."

Cousteau's intellectual hero, he says, is Bertrand Russell, the British philosopher, mathematician and ardent pacifist who died in 1970.

Now, Cousteau says, he is writing "quite a book," but not about the oceans. It will be, he says, "my opinions. It's about what I think . . . The only difference between the taxi driver and me is I have an opportunity to see the world and have time to think. He is drowned by the demands of the world. I'm fortunate to have that kind of life, and I want to share it."

Pause. Smile.

To the bridge!

Calypso, a 141-foot converted mine sweeper donated privately to Cousteau in 1950, is such a nifty little world unto itself that you immediately feel happy and at home on board, and sad on leaving. The crew, mostly French, is headed by Capt. Albert Falco, a short, dark man with powerful diver's shoulders who has been with Cousteau for 33 years. "My father's right hand," says Jean-Michel. Falco says it is great to be at sea again after months in dry dock for repairs.

Calypso, he says in his unfailingly cheerful polyglot, is now "ready for tour du monde!" He adds thoughtfully, "Fantastique life with Captain Cousteau!"

The crew mostly look like rugged young sea gods, and they seem to be having a great time.

In the foggy postdawn off Mount Vernon, they lower the Zodiak rubber boats and zoom in to pick up Cousteau and the Turner film crews.

Bob Braunbeck, who pilots the little Hughes 300-C chopper perched on a special high platform, warms it up.

There is diving gear here and there, a decompression chamber, fuel tanks, a device that converts sea water to potable water. There used to be a three-ton stainless-steel wine tank, but Cousteau got rid of that because the crew switched to beer in hot climates anyway.

For this trip up the Potomac, the soucoupe, the little underwater diving saucer that Cousteau invented years ago, is not aboard. It is still being repaired in Norfolk.

As all this activity gets under way, Joe Cramer, a mechanic who has been a Calypso crew member for four years, begins bouncing up and down on his toes and laughing.

Why? he is asked. "This is so much fun!" he replies. Cousteau has said he chooses his crew for competence, but they must be "good guys." It is a team effort, and most decisions are made jointly by the crew.

As Calypso begins steaming from Mount Vernon to Washington for Riverfest, one of the following tall ships, the Chesapeake, runs aground. Leon Schertler, a private consultant hired by the District to advise the city on tall ships, explains Riverfest to Cousteau, talking about how the Potomac is cleaner although it is still not advisable to swim in it.

Cousteau jokes that, "At 7 o'clock, when Washington inhabitants take showers, the water level goes up."

Schertler confides to a reporter that, "Two weeks ago, Marion Barry didn't know who Jacques Cousteau was. Then I started to brief him. When he heard there were going to be television cameras all over . . ."

No matter. Jean-Michel says that when singer Denver, a board member of the Cousteau Society, suggested a few years ago that the oceanographer team up with broadcaster Turner, Cousteau said, "Who's Ted Turner?"

"It's a very fine relationship," says Jean-Michel. "Unlike in the past, we have total editorial control. They never put their nose into it."

"Only once," Cousteau corrects his son, but doesn't elaborate.

"Apart from that," Cousteau goes on, "what I like in Turner is he's consistent with his ideas . . . Where he has pledged to do something, he does it."

At Turner's Mount Vernon party last night, 2,000 guests crowded around Cousteau, his family and Turner as the evening light faded over the Potomac. Celebrities among the guests included Jose Ferrer, Stefanie Powers, Jimmy Buffett, Hoyt Axton and Ben Vereen.

Calypso had pulled up to the dock, but guests weren't allowed on board. There were tents on the lawn, balloons, a gentle breeze.

Before the speeches, Mayor Barry and his wife Effie crowded up to have their picture taken with Turner.

Meanwhile Cousteau, this time dressed in a white duck leisure suit, was telling reporters that he wouldn't mind taking a trip in the space shuttle, while nearby his wife Simone was explaining how much she hates giving interviews.

"I hate it," she said. "I don't look like Greta Garbo, no?"

Later during the speeches, Jean-Michel introduced his mother as "the shepherdess" of Calypso who acted as a loving mother to the entire crew. He said that during one of the Conshelf underwater living experiments, Simone had lived underwater for one week. "With five men!"

As Calypso eases up the channel toward a dock lined by thousands of people waiting to greet Cousteau, the general hubbub and noise level gets so high that Cousteau covers his ears and groans with a pained look on his face.

"All these noises! Owwwwwwwwww!" he says.

Frenetic TV crew people rush in and wire the grand old man for sound.

Calypso approaches the dock.

Cousteau combs his hair.

"Zheek, we'd like you to be out on the bow when we arrive!" shouts a Turner producer.

The TV guys frantically maneuver their cameras into position. The roar of the crowd can be heard as Calypso eases up to the dock. Braunbeck is in the chopper buzzing around just over the water next to the crowd, expertly whipping everyone to new levels of enthusiasm.

"Are you ready?" shouts the producer. "One second, one second . . . Okay! Come on out!"

Cousteau steps out onto the wing deck beside the wheelhouse and raises his hands to the people.

That smile!