Early in the sixth race of the 1983 America's Cup series, Liberty skipper Dennis Conner, stuck in a wind hole, helplessly watched Australia II speed past him. Conner turned to his 10 crewmates and asked a question no one wanted to hear.

"Anybody got any ideas?"

Said mainsheet trimmer John Marshall, "When D.C. asks for ideas, you're in deep trouble."

At noon Saturday, Conner and his mates will try to dig out of the deepest trouble a cup defender has ever encountered. Tied, 3-3, in the best-of-seven final series for yachting's most prestigious prize, they are on the verge of becoming the first Americans to lose the cup in its 132-year history. No foreign yacht has even been in position to win in 24 previous challenges, and Liberty is thought to be defending the longest winning streak in sports.

(Not all of the race will be televised. However, NBC and CBS will televise live reports throughout the day, and ABC will have a live report on its Wide World of Sports show at 5 p.m.)

One thing Conner probably will try in the final race is a lighter configuration. After Australia II won by 3 minutes 25 seconds Thursday, the worst defeat ever for a U.S. 12-meter, Conner sent Liberty across Narragansett Bay for revisions.

Tonight she is due back in Newport with at least one option in hand for the finale. Liberty has removable lead ballast weights just above her keel; Conner had about 1,000 pounds of them removed and the boat was remeasured and recertified as a 12-meter in this lighter configuration.

As a lighter boat she would be permitted to carry larger foresails, Conner said. Sailmakers were working tonight to to increase the size of existing sails.

Conner will use the bigger sails Saturday, he said, if late-hour weather forecasts indicate light winds under about 12 knots, in which Australia II has proved nearly unbeatable.

If the breezes stay strong, Conner said, he will replace the lead ballast and sail Liberty as she's been configured for the first six races, hoping to eke out competitive speed and win on tactics.

The competition, long considered an effete exercise for the rich, suddenly has captured the fancy of the nation. Today Conner received a telegram from President Ronald Reagan saying, "Nancy and I just want you to know how hard we'll be rooting for you in the final race of the America's Cup."

Added Reagan, "This 'yacht race of the century,' as you call it, is the moment we've all been waiting for and we and the American people wish you Godspeed."

Australia II, with her radical, winged keel, arrived at her lofty spot in yachting history by being faster than Liberty. There is no argument in any camp about that.

"No conventional 12-meter in the world can keep up with her," said a top official in the U.S. effort.

The advantage may be no more than one-hundredth of a knot, said Australia II skipper John Bertrand, but in the snail's-pace chess game that is yacht racing, where a 24.3-mile race takes almost four hours, that tiny edge can be decisive.

By attaching five-foot-wide horizontal wings to the bottom of Australia II's keel and concentrating weight just above the wings, designer Ben Lexcen achieved a breakthrough.

The changes provided stability and allowed him to build a light boat--about 4,500 pounds lighter than Liberty--that flies in gentle air yet stands up to a stiff breeze.

Australia II is faster in practically any condition, yet Conner and Liberty have won half the races so far, twice profiting from Australian gear breakdowns and once from a magnificent tactical performance in which Conner edged the challenger by 47 seconds.

But Bertrand won the last two races easily to rally from a 3-1 deficit. The sense here is that he has calculated his advantages and how to use them.

So has Conner, whose notoriously aggressive tactics in this final race for the cup worry his opponents more than his last-minute bid for boat speed. Australian syndicate chief Alan Bond, who is pursuing the cup for the fourth time in 12 years, said he fears Conner will try to force Bertrand into a collision at the starting line, then try to win the cup in a protest hearing.

Conner, 41 and in his third cup as a starting helmsman, has bested the less experienced Bertrand at the start of the last three races. Bond had Bertrand out today practicing starts.

"We went through a lot of maneuvers to see what Dennis Conner could do to foul us out," said Bond, "and what we could do to counteract if he came up and hit the boat."

Conner, looking drained, stopped by Liberty's empty dock briefly this afternoon on a brilliant, breezy, fall day. He said his weather experts were predicting a softening of the breeze by Saturday but that he would wait for later reports before deciding in which mode he would sail Liberty.

He said the lighter configuration is one he and the crew tested earlier in the summer during trials to pick a defender, so he knows what to expect from the revised boat. Less weight will provide optimal performance at wind speeds of about 12 knots rather than 14 or 15 knots, he said.

Altering 12-meters for predicted weather conditions has long been regarded as folly in these waters, where weather patterns shift unpredictably and suddenly. But with only one race left and not a whole series, Conner said his aim is to optimize performance for the day of the race.

"They are under pressure," said Australia II syndicate manager Warren Jones. "I'm delighted that we're not the ones trying to find boat speed at this point." Added Jones, with well chosen words and a twinkle in his eye, "For their sake, I hope the winds stay light."

If Australia does what no challenger has done in 132 years, the silver America's Cup is to be unbolted from its showcase in the New York Yacht Club and presented to the Royal Perth Yacht Club on Monday in New York.

RPYC Commodore Peter Dalziell said the club would then accept challenges for the next America's Cup series in January 1987.

In Perth.