We have seen the secret keel, and it is blue.

Australia II, with its controversial, winged keel, today won the right to be the 25th challenger for the America's Cup with what modern yachties call "a horizon job" over Victory '83. She left her British rival so far behind in a 3 minute 19 second victory the loser seemed almost a mirage in the haze at the finish.

The victory gave Australia II her final required victory as she completed a 4-1 drubbing of Victory in the trials to select a challenger. Her average margin in the last four races was 3 minutes 25 seconds, an eon in 12-meter racing. With the victory, Australia II gains the right to compete for the Cup, which the United States has never lost in 132 years, when final races begin Sept. 13 against U.S. selection Liberty.

Most observers believe Australia II's shocking superiority over all foreign rivals is due to her radical keel, which allows her to turn faster, point closer to the wind and by virtue of which she finished the long summer of racing with a stupendous 48-6 won-lost record, engendering deep concern among officials of the New York Yacht Club and defending skipper Dennis Conner.

But what does the keel look like? Until today that was a deep, guarded secret as the Aussies draped skirts and placed protective boards against Australia II's sides every time she was raised from the water, and protected access to their dock with armed guards.

But there are celebrations when milestones pass, and today there was a great cheering and champagne-popping celebration at Australia's dock, complete with fistfights, beer guzzling, Men at Work tapes and dunkings of crewmen.

Victory '83's crew joined in and her crewmen took dunkings, too. Two of them thought that, since they were in the water anyway, they might just swim over under the drapes and grab a quick look.

John Longley, a huge Aussie deckhand, went in hot pursuit and dragged the interlopers out, crowing, "They've promised not to tell."

But while the crowd was guffawing, some news hounds took the opportunity to slip around back, climb some scaffolding and found themselves gazing upon the great yacht's secret petticoats from above.

"It's blue," they said in a single voice.

And indeed it is. Australia II's keel, at least the controversial bulbed and winged parts of it, is painted blue in contrast to the white of the rest of the yacht, perhaps in an effort to conceal the intricacies while it's submerged.

The leading edge of the keel angles forward, opposite the normal 12-meter configuration, and appears to end in a slight bulbousness at the forefoot.

The wings are dramatic. Delta-shaped and perhaps five feet across, wingtip to wingtip, they emerge from the foot of the keel about halfway back and spread out like a giant blue glider.

It is "very much like what I drew three months ago," said Sail Magazine reporter Jay Broze, whose publication's illustration has been widely circulated and became the general consensus of what the keel looks like.

So that secret is finally out, what shreds were left of it.

The secret that remains is exactly how fast the keel and the slimmed-down underbody that accompanies it are going to make the Aussies in relation to Conner's conventionally-designed 12.

Today on the race course in 10- and 12-knot breezes and smooth seas the Aussies showed skillful boat handling for as long as they needed it, which wasn't long.

Australia II turned dizzyingly fast circles to shake the British boat before the start, then marched off to a 1 minute 18 second advantage by the first upwind mark 4 1/2 miles away. Twenty miles and four hours later at the finish she was a quarter-mile ahead and crossed the finish alone to the horn blasts and cheers of a sizable spectator fleet.

Syndicate chief Alan Bond, a millionaire financier from Perth, quickly jumped aboard Australia II along with syndicate manager Warren Jones. Bond, in his fourth attempt to wrest the Cup from the United States, greedily grabbed the yacht's wheel and toasted his crew with Swan Lager.

They sailed the 15 miles home under full spinnaker and were greeted by a raucous crowd.

Bond predicted his lads would take the Cup, 4-2, in the best-of-seven Cup series beginning next week.