Halsey Herreshoff, yacht designer, bearer of an impeccable yachting name and crewman aboard the 1980 America's Cup champion Freedom and on probable 1983 defender Liberty, has seen enough.

"If the closely guarded, peculiar keel design of Australia II is allowed to remain in competition, or allowed to continue to be rated without penalty," wrote Herreshoff recently in a memo to the New York Yacht Club, "the yacht . . . likely will win the America's Cup in 1983."

Now, perhaps spurred by Herreshoff's dire prediction, the New York Yacht Club says it's seen enough, too.

Convinced that Australia II's mop-up of all competition in cup trials this summer is due to an unfair underwater advantage, the NYYC, which has held the cup without a loss through 24 challenges and 132 years, has formally protested the yacht's rating as a 12-meter.

In a letter posted last week, the NYYC's America's Cup Committee requested a ruling from the International Yacht Racing Union "to determine if the yacht Australia II has been fairly rated."

So begins what promises to be every bit as controversial a dispute as the one the New York Yankees precipitated when they tried to steal George Brett's pine-tar-bat home run.

The parallels are interesting because the protesters, host New Yorkers in both cases, were aware well before they complained that their foes were playing with peculiar tools, but chose to wait until the game was on the line before raising the protest. "That was a mistake," admits Herreshoff.

The yacht club's summer-long delay in raising the issue of the legality of Australia II's wing-shaped keel sparked immediate cries of foul. "We are amazed at the lengths to which the New York Yacht Club is prepared to go in endeavoring to avoid competing with Australia II," thundered Australian syndicate chief Alan Bond yesterday.

In case any yachting fans have been asleep in a burrow, here is the situation:

The Australia II challenge, the Bond group's fourth straight attempt to wrest the cup, arrived in Newport this spring sheathed in secrecy.

The new boat had a "revolutionary" keel and underbody, said designer Ben Lexcen, and to make sure the design wasn't copied he had a canvas skirt set up around her when she was at the dock and an armed guard posted to keep prying eyes away.

All facets of the boat were measured, as were all 10 yachts competing for the cup, by a three-man international committee when she arrived. She was certified a 12-meter and no protests were raised.

Since her arrival, Australia II has raced the other six foreign boats seeking the right to challenge for the Cup 40 times and lost only four times. Three losses were attributed by observers to fluky winds, and the fourth was a forfeit when a crewman was injured before a race.

In short, Australia II has run roughshod over the largest and most impressive array of challengers ever assembled, and seems certain to win selection as the challenger for the final cup series against the American defender starting Sept. 13.

By contrast, the three American boats seeking to defend the cup--Liberty, Courageous and Defender--have been hammering away at each other, and only in the last few weeks has Liberty, defending Cup champion Dennis Conner's boat, begun to show general superiority.

Against this backdrop of evident peril to U.S. retention of the cup, the New York Yacht Club has finally spoken up. Australia II, said the NYYC in its letter to the IYRU, has been in a class by herself. "On the three windward legs" of her 40 races, "she gained a total of 1 hour 1 minute 56 seconds" over her foes, wrote the club. "When normal 12-meters . . . usually finish within one minute of each other, Australia II's record is all the more demonstrative of the advantage she has."

The perceived source of this superiority is the strange keel with its bulbous protrusion at the forefoot and wings reportedly five feet across, tip to tip, at the aft end.

According to Herreshoff, the wings serve to increase the draft, or depth, of the boat when she is heeled over during sailing, giving Australia II what he and the NYYC regard as an unfair edge.

Although the wings are parallel to the surface of the water when the boat is upright, said Herreshoff, when she heels to one side under sail, one of the wings winds up pointing down, effectively extending the depth of the keel.

Herreshoff believes that factoring in that advantage under way, Australia II should rate at about 12.75 meters instead of 12. If the IYRU agrees and, in a remeasurement, Australia II is found to rate in excess of 12 meters, she would have to reduce some other dimension to compensate, most likely sail area, and her speed advantage would be diminished or lost.

Perhaps more significantly, other foreign challengers already have indicated if changes are mandated for Australia II they would protest her selection as the challenger on grounds she was unfairly rated during the challenge trials.

Designers of two U.S. contenders, Johan Valentijn of Liberty and Dave Pedrick of Defender, said this week that Australia II has shown distinct superiority to conventional 12-meters in the speed with which she changes tacks, her ability to accelerate and in her upwind sailing speed.

The question now before the IYRU's keel-boat technical committee is whether Lexcen's stunning advance in 12-meter design is legal. The NYYC based its demands for revision on a stipulation in the 12-meter rule that requires review by the governing body of any "peculiarities" of construction or design that would give a boat an unfair advantage.

"They seem to have a pretty good case on that," said Jeff Spranger, editor of the America's Cup Report and a veteran cup watcher. "The keel is certainly a peculiarity." Said Valentijn, "I wish I'd thought of it."

Just how peculiar it is, and whether it can slip through a loophole in the 12-meter rule, is anyone's guess. Security for Australia II has been so good that no one outside the Australian camp claims 100 percent certainty of what the keel and underbody look like, exactly. The international measurers are the only objective observers who have seen the hull in detail, and they aren't talking.

The best informal guess so far seems to be Sail magazine's depiction of the hull in its August issue, which editor Keith Taylor claims "is about 90 percent accurate, we think."

Sail's drawing is of an odd hull, indeed. One irreverent observer said, "It looks like a commode." But if Australia II succeeds next month in seizing yachting's most treasured jewel from the nation that has never lost it in almost a century and a half, it will be a shape quickly seen 'round the world.

The IYRU's decision on review and remeasurement is expected within a week. Australia II is scheduled to resume racing Aug. 11 against semifinalists Victory '83 from Great Britain, Azzurra from Italy and Canada I.

The three U.S. boats will begin their final competition Aug. 16 for the right to defend. Both sides must name a final contestant by Sept. 8.