SAN DIEGO (AP) _ The San Diego Yacht Club, its plans for a 1991 America's Cup regatta capsized by a court ruling, said Wednesday it would accept New Zealand's challenge to race for the cup next year but exclude all other competitors.

''This next event may not be America at its most skilled and it won't be the rest of the world at all, unfortunately. But that is the challenge,'' said Tom Ehman, a vice president of the Sail America Foundation, which is managing the cup defense for the yacht club.

In a news conference, Ehman and yacht club Commodore Dr. Fred Frye outlined their response to last week's New York state court ruling, which upheld a challenge by New Zealand merchant banker Michael Fay.

Fay based his challenge on a literal interpretation of the Deed of Gift, a 100-year-old document governing America's Cup competition.

Ehman said Sail America and the yacht club were basing their exclusion of other competitors on the same narrow interpretation of the deed and the court ruling.

''San Diego will not consent to other challenges under the terms of this challenge,'' Ehman said. ''If that somehow changes, perhaps we would, but currently the answer is no, capital n-o, no.''

Fay called for a three-race series in 90-foot waterline boats, legal under the deed but a radical departure from the 12-meter yachts common to America's Cup competition for the past 30 years. The 90-foot boats are roughly twice as long as 12 meters.

''The judge told us that Michael Fay's challenge was a valid challenge and that we must defend on the terms of that challenge or forfeit the cup,'' Frye said. ''We have no intention of forfeiting this cup.''

Though pleased the yacht club will meet him on the water, Fay said he was disturbed by the decision to limit competition to the United States and New Zealand.

''We don't think it's the right decision or a popular one, and it's inconsistent with everything they've been saying about what's important for the success of the America's Cup,'' Fay said.

The San Diego Yacht Club, which won the cup last February when Dennis Conner skippered its Stars & Stripes entry to victory over Australian defender Kookaburra III, had received 21 challenges from 10 countries for the planned 1991 America's Cup regatta off San Diego.

Ehman did not name a site for the race with Fay. He said the seven-member America's Cup Committee, designated earlier by the yacht club and Sail America earlier, would pick a site and announce it at least 90 days before the next America's Cup race.

Frye said the venue for the match race with the New Zealanders, expected to take place in August or September 1988, would be wherever conditions would be best suited for a successful cup defense.

That could mean Hawaii, San Diego, Santa Cruz or San Francisco or any other of a number of locations.

''If we can have a reasonable assurance that we can win it in San Diego, then we'll race it in San Diego. But if it's a 5 percent chance in San Diego and say 40 percent in Santa Cruz, then we've got to race in Santa Cruz,'' Frye said.

He called the selection of venue ''wide open.''

Fay's Mercury Bay Boating Club has already started building a 90-foot boat designed to sail in light wind conditions off San Diego, prompting San Diego officials to consider the venue change.

''It's certainly our goal to get rid of this (New Zealand challenge) as quickly as possible so we can go on with conducting a proper America's Cup regatta in 1991,'' Ehman said.

Fay said he thought San Diego officials were being unfair by structuring their response to try to ensure a successful defense.

''We don't have to and we'll never have to race under the conditions set down by Sail America,'' Fay said. ''All we have to do is sail under the conditions set down by the rules of competition. San Diego can't take onto themselves the power to unilaterally impose conditions on the challenger.''

The two sides are expected to negotiate differences over rules of the competition in coming weeks.

Because a $1.2 billion economic windfall from the America's Cup is at stake, the city of San Diego directed its attorneys Tuesday to appeal the New York court ruling upholding Fay's challenge.

Ehman said Sail America and the yacht club have yet to receive a final order from the New York court to implement its ruling. He said no decision would be made on an appeal by the Yacht Club until they receive that order, which is expected in the next few days.