Although the final races in the 23d America's Cup won't begin until Sept. 13, at least eight 12-meter yachts will be in Newport from mid-June, vying to be a finalist for the oldest international sports trophy still awarded.

At least four American boats will be racing for the right to defend the Cup first won by the yacht America in 1851 and never lost by the U.S. They are:

Courageous, the 1974 Cup, winner, designed by Olin Stephens and sailed this year by Ted Turner.

Enterprise, a new Stephens boat sailed by Lowell North.

Independence, another new boat designed and sailed by Ted Hood, winner of the Cup in 1974 when he skippered Courageous in the race against Southern Cross, an Australian boat.

Intrepid, another Stephens design, which won the Cup in 1967 and 1970 and barely lost to Courageous in the 1974 trials. As then, Intrepid will be sailed by Gerry Driscoll. She is owned by the same syndicate as Enterprise.

Preliminary trials are June 18-25, observation trials July 16-27, final trials Aug. 16-Sept. 5.

The foreign challenger will be chosen from among these four boats:

Australia, a new design by Bob Miller, designer of Southern Cross.

France II, a new boat designed by Andre Mauric and owned by Baron Marcel Bich, who lost to Australia's Gretel II in 1970 and to Southern Cross in 1974.

Gretel II, also from Australia, a modified version of the boat designed by Alan Payne that lost to Intrepid in 1970, but was widely considered to be the faster boat.

Sverige, a new design from Sweden by Pelle Petterson, the first Scandinavian entry into the competition.

Races among the four foreign boats to select the single challenger for the Cup begin Aug. 5, continue with a second series Aug. 15 and conclude with a series Aug. 25.