Amid the sound of exploding cannons, blaring horns, firecrackers and thousands of cheering voices. Courageous and her skipper, Ted Turner, were welcomed back to Bannister's Wharf today after successfully defending the America's Cup.

Courageous completed a 4-0 sweep of the best-of-seven series for yachting's most cherished prize, beating challenger Australia by 2 minutes 25 seconds in moderate winds that dropped off to light late in the 24-3-nautical mile race on Rhode Island Sound.

Courageous' victory, achieved when Turner again masterfully squeezed ahead on the leeward side and took a commanding lead on the first leg, was not nearly as interesting as the celebration that followed.

Thousands of spectators lined lawns and rocks along the harbor to catch a glimpse of the aluminum-hulled yacht that has been called the fastest 12-meter designed, and to give a resounding heroes' welcome to her flamboyant skipper and spirited crew.

Many of the onlookers wore T-shirts adorned with photos of Turnover and the words, "Captain Courageous." Some waves banners, and hordes swarmed around a hugh lawn painting that spelled out "U.S. 26," Courageous' sail number.

In 1974, with Ted Hood at the helm. Courageous won four straight races from the Australian yacht Southern Cross in the 22d challenge for the 126-year-old cup that the United States, represented by the New York Yacht Club, has never lost. But the reaction was nothing like this.

Turner, the charismatic 38-year-old Georgian who owns baseball's Atlanta Braves and basketball's Atlanta Hawks as well as a communications empire, has brought his good ol' boy personality and a large measure of popular appeal to the stuffy world of yachting.

Today a crowd of several thousand jammed the usually tranquil Newport Habor, pressing as close as possible to Bannister's Wharf, where Courageous and syndicate sister Independence have been docked since trials to select an American defender started three months ago.

They shoved against the white trestle that leads out into the pier, hung from buildings, clumbed on roofs of nearby shops and mobbed adjacent wharves, straining to see the jubilant reception Courageous' crew got from those privileged to get by uniformed guards and greet the victors at sea.

Young and old, male and female joined in the noisy welcome, which must have horrified the confirmed stuffed shirts on the committee boat. The madcap scene was equal parts Mardi Gras and fraternity house blowout.

As Courageous came in, five deafening cannon blasts from the Revolutionary War frigate Rose greated her, drowning out the cacophony of horns, smaller ceremonial guns, noisemakers and screeching lungs.

Turner and his 10 crewmen were hauled off their handsome boat, tossed into the water and doused with champagne.

After his victory dunk, Turner was hoisted to the shoulders of the crowd and jovially carried down America's Cup Avenue, gulping champagne, puffing a huge cigar, reveling in the adulation.

When they got to the Armory on Thames Street, site of a press conference that turned out to be more of a raucous party, Turner and his tactician, Gary Jobson, were met by the Australian crew, who sang "Dixie" and slapped Turner on the back.

The Aussies also had taken a salt water bath when they docked at Newport Shipyard. Alan Bond, head of the owning syndicate, and Noel Robins, Skipper of Australia, were carried to the armory on the shoulders of their crewmen, who spilled as much beer and champagne as they guzzled and sang lively choruses of "Waltzing Matilda."

Their green-and-gold uniforms still dripping from their cold swim in the brine, the Aussies danced on the podium, drank ribald toasts and loudly talked about "raising another $2 million and trying again in 1980."

Bill Ficker, the winning skipper on Intrepid in 1970 was was appointed by the New York Yacht Club to moderate press conferences and censor potentially embarrassing questions, failed abjectly in his attempts to bring order to the tumultuous goings-on at the armory.

As TV lights glared off his shaved head, Ficker reached over and removed the champagne bottles Turner had brought with him. Turner - feigning drunkenness in word and gesture - climbed under the table and grabbed them back.

"While I have the microphone, which won't be long," said Turner, slurring his drawl, "I want to say I've never raced against such good sportsmen as my friends from Western Australia . . . I've never enjoyed sailing against anyone as much. They are the best of the best."

Even those who deplore Turner's boozy and bawdy behavior, who refer to him as "Terrible Ted," "The Mouth of the South," and "The Pirate of Peachtree Street," admit he is a superb sailor.

Courageous proved conclusively that she was the faster boat, with better sails and a more accomplished crew.

Courageous won the four races by margins of 1:48, 1:03, 2:32 and 2:25, the first and last in moderate airs, the middle two in light weather.

She also had a lead of humiliating proportions, perhaps 20 minutes, in a race that was nullified because she failed by 550 yards (about 3 1/2 minutes) to finish within the 5 1/2-hour time limit.

Today, on a warm and sunny but rather hazy afternoon Courageous and Australia crossed the starting line in a dead heat. But as she has done throughout the series, Courageous quickly got in position to make the most of 14-knot westerly breezes that later shifted slightly to the south and dropped to nine knots at the finish, 3 hours 35 minutes later.

As he had done so masterfully all summer, first in trials against Independence and Enterprise and then against her cup rival from the Sun City Yacht Club, Turner pinched up from the leeward and then quickly tacked on his opponent's bow, forcing her to tack away to escape his backwind.

Having thus taken the lead, Turner performed all the defensive tactics of match racing perfectly and gradually sailed away to leads of 0:44, 0:48, 0:56, 2:11, 2:35 and 2:25 at the six marks.