Down at Bannister's Wharf, where members of the crew of Courageous all but whistle while they work, three young men were scrubbing the white aluminum hull that skipper Ted Turner says is sanded "smoother than a baby's bottom."

The sleek 12-meter yacht that takes a 1-0 lead over Australian into Thursday's second race in the best-of-seven series of sailing's grandest prize, the American's Cup, was up on its hoist.There was no racing today, Australia having requested a lay day after its 1 of the 23d challenge Tuesday.

They probably wouldn't have raced, anyway, because the wind, which gusted up to 40 knots this morning, whipped the waters of Rhode Island Sound into a formidable chop.

But despite gloomy skies and a few raindrops, the crewmen of Courageous were buoyant, even jovial as they went about their daily routine, secure in the knowledge they are now favored to defend in four straight races the big silver trophy that America has never lost since it was introduced in 1851.

Courageous' dock has the air of a smooth, supremely confident organization, even though Turner - the flamboyant and boisterous good ol'boy from Atlanta who has become the unlikely standard-bearer of the staid New york Yacht Club - had not yet arrived.

This is the way it has been since the trials began in June, local aficionados attest. Courageous, the experts say, may have the best 12-meter crew since Vim in the 1958 American Trials.

On the water, they execute with swift precision, changing sails with bewildering frequency, but so efficiently that their maneuvers often go unoticed.

"They're all first-rate sailors. They can do anything with that boat. It's beautiful to watch," marveled one observor of every America's Cup since 1937.

Their spirit is similary enviable. Six of the 11 men on Courageous - Turner, tailers Richie Boyd and Carl Helfrich, sewer man Conn Findlay, sailmaker-trimmer Robbie doyle, and man for all seasons Mary O'Meara - are veterans of the disastrous Mariner campaign in 1974, good men who suffered with a dud of a hull.

"I think everybody on Mariner wanted to come back and vindicate themselves," said Doyle, 28, who was recently made president of Ted Hood's world-renowned sailmaking operation in Marblehead, Mass.

Courageous, which whipped Southern Cross by the almost customary 4-0 score with Hood at the helm in 1974, was originally considered just a tough sparring partner this time for syndicate sister Independece, which Hood designed and captained.

But Courageous piled up a convicing 26-9 record against Independence and Enterprise (skippered by Lowell North, Hood and Doyle's sailmaking competitor) in all kinds of weather, earning the right to defend and a reputation as perhaps the fastest 12-meter ever built.

"It's been sweet for all of us from Mariner," Doyle said, "because in America's Cup your reputation is on the line. You know that in the finals each country shows up with the best it can produce. People will look at your performance and say. "This is the best this individual can do."

When Turner arrived at bannister's at 10:30 this evening, he was carrying a note on White House letterhead.

"Hey, look at this - a handwritten note from the President," he yelled over to his trusted tactician, Gary Jobson.

Turner read aloud, in the peculiar drawl that is tinged with the clipped inflection of brass buttons: "Congratulations to you and the crew of Courageous. I am proud of you all, and all Americans - Yankees and Southerners - with you well in the coming races, Jimmy Carter."

Later Doyle, the Yankee from Marblehead and Harvard whose maginificent sails Courageous has flown so successfully - Turner admiringly calls his sailmaker "a magician" - echoed the teamwork theme.

"I've gotten a lot of credit, but the reason this operation works is that everbody does his job well," he said. "I hardly have to do anything as far as maintenance of the boat. Marty O'Meara has taken care of everything in my area so I could spend three of four hours a night concentarting on the sails.

"Turner's not fanatic about overseeing the tinkering with the boat. He figures his job is just to sail it. When he leaves at night, he knows Richie Boyd will have everything shipshape in the morning.

"It's the same with the sails, Doyle continued. "We have a small inventory, maybe one-third of the number Enterprise and Independence had, but we perfected what we have. Hod and North were always looking for the breakthrough sail, whereas I felt getting the most out of what we had was the real breakthrough."

"It takes a little courage to change sails on a 12-meter as often as we do during a race, but we've gotten it down to a science. We almost always have the right sails up, which makes me look good."

The opening race suggested that there is not a great deal of difference in the hull or boat speed of the two yachts, so sails and crew should be the major factors. And it is a measure of Courageous' confidence that Doyle hopes Thursday brings light weather, conditions in which Australia performs best.

"If the wind really blows, we should be much faster," he said, nothing the forecast of 10-to-25 knot winds from the north-northwest, a prospect that must distress Australia skipper Noel Robins.

"But I personally hope it's light," concluded Doyle. "We did awfully well against Independence and Enterprise in light weather all summer, and I think we can take Australia in the conditions she likes best. I'd like to answer that question."