Australia II won again on the America's Cup race course today, sealing a spot in the challenger finals starting Aug. 28, and afterward won a ringing endorsement for her winged keel from her principal competitor among the foreign fleet, Britain.

The U.S. Yacht Racing Union and New York Yacht Club contend the wings at the base of the Aussie keel are illegal because they increase her depth in the water unfairly when she's underway.

USYRU is seeking a supporting ruling from the International Yacht Racing Union.

But tonight British syndicate chief Peter de Savary, whose Victory '83 is expected to compete with Australia II in the final series for the right to challenge for the Cup, said the IYRU has already advised him the keel is legal. He cited correspondence with the IYRU his group initiated last month when the British were considering trying a winged keel.

De Savary said he wrote to IYRU chief measurer Tony Watts in July to ask if keel wings were permissible. The answer, said de Savary, was yes, as long as they did not exceed "static draft."

"Static draft" means the depth of the keel when the boat is in an upright position. The response from the IYRU, he said, was that as long as keel wings are horizontal to the base of the keel, as they are on Australia II, they are allowable.

De Savary suggested that the Americans should drop their protest and get on with racing on the water, rather than prolonging the legal dispute. His endorsement was considered significant in that it isolates the U.S. as the only complainant, even though four other nations have had to compete against the Aussies in this Cup campaign.

The IYRU, responding to USYRU entreaties, will convene a special meeting Aug. 30 to determine whether to seek a ruling from its Keelboat Technical Committee on the legality of Australia II's keel.

In racing today among the foreign fleet, Victory '83 lost to Italy's Azzurra, putting the British record at 5-2 in the nine-race semifinal series.

Azzurra overcame Victory's nine-second lead, led by 10 seconds at the first weather mark and won by 50 seconds.

Azzurra is 3-4, and Canada, which lost to 6-1 Australia II today, is 0-7 and out of the running.

Two boats will advance to the final challenge round and the winner of that competition will face the U.S. defender Sept. 13.