America's Cup syndicate chief Peter de Savary, whose British yacht is battling Australia II for the right to be this year's challenger, secretly put wings like Australia's on his boat's keel today, then protested that the official U.S. measurer who approved the plan blew his secret.

De Savary said he decided Sunday night to try "winglets" on Victory '83. To make sure they were permissible, he said, he asked Mark Vinbury, one of three international measurers qualified to judge, to check them this morning.

De Savary said Vinbury approved them and promised to keep the secret. But the syndicate chief produced a copy of a letter dated today and signed by Vinbury notifying the U.S. Yacht Racing Union of the change and challenging its legality. USYRU promptly protested to the International Yacht Racing Union.

De Savary was furious, maintaining confidentiality was violated by a measurer he presumed to be impartial.

Vinbury was unavailable for comment, but the USYRU issued a statement indicating the measurer was following normal procedures and USYRU chief Ken Weller said he had asked de Savary if he was actually there when Vinbury checked the keel and de Savary "said he was not."

De Savary said he had hoped to use the winglets in light-air conditions like today's, and said under the rules he would not have been required to notify his competitors. But once the secret was out, he said his advantage was nearly nullified.

The developments put another hot pepper in the controversial stew that has been stirred all summer by the Australians. They came to Newport with a secret, bulbous, winged keel and have wiped out all their competition so far.

The New York Yacht Club has held yachting's dearest prize, the America's Cup, for 132 uninterrupted years and regards the Aussie keel as a threat. NYYC and the USYRU have mounted a campaign to discredit the keel and have it disallowed under the rules before the Sept. 13 start of the cup races.

De Savary has been a steady supporter of the Aussies' right to compete and now has joined their camp.

But he said the wings didn't do much for Victory's speed. "Actually, she was about three-tenths of a knot slower upwind," he said, and that was the point of sail on which he hoped for improvement. De Savary said he would continue experimenting.

Victory '83 lost to Australia today, but finished second in the challengers' semifinal elimination round with a 6-3 record. Australia II was 8-1. Italy's Azzurra (4-5) and Canada 1 (0-9) were eliminated. The two remaining yachts will begin final elimination racing Aug. 28.

Meanwhile, an anxiously awaited light-air showdown between U.S. rivals Courageous and Liberty all but vanished today in thick fog.

The Americans, racing a couple of miles away from the foreign course, were swallowed up by a fog bank and had to cut racing short. Before they quit, Dennis Conner won a 10-mile shortened-course race in Liberty, and John Kolius in Courageous eked out a narrow victory in a 4 1/2-miler.

The selection committee overseeing U.S. racing quickly announced a rematch Tuesday, setting back by a day the return to competition of the third U.S. contender, Defender.

Members of the New York Yacht Club Selection Committee want to see these two boats battle in light air after having watched Courageous beat Liberty by close margins twice in fresh breezes in their only other meeting in the finals.

Courageous is 7-2 in the final trials. Liberty is 3-3, Defender 1-6.