The America's Cup defense effort, plagued for two years by lack of funds and general public disinterest, suddenly is looking up.

Disclosures last week -- one official and one unofficial -- gave credence to two organizations gearing up to defend yachting's top prize against the best of 11 or more challengers in San Diego in May 1992.

The Beach Boys Syndicate announced yesterday it was buying France I, one of five boats built so far in the new, 75-foot America's Cup Class, as a training boat and would ship it to San Diego to begin trials around Jan. 1.

The acquisition will make the Beach Boys Syndicate the first U.S. team with a boat in the water, a crucial first step for fund-raising and training. The syndicate plans to build two more boats for the Cup.

Additionally, Annapolis's Gary Jobson, a veteran of three Cup campaigns, signed on last week with billionaire Bill Koch, who apparently has decided to back a well-funded defense campaign. Jobson said the team would include Olympic gold medalist Buddy Melges and 1989 yachtsman of the year Larry Klein, who will abandon his underfinanced California-based effort.

Jobson said a four-year design and development program for Koch's new maxiboat, Matador Squared, produced a boat that is extremely fast -- a breakthrough in hull and keel design. Koch believes the technology can be transferred to a Cup boat and is willing to back it financially through at least the early phases, Jobson said.

Koch and Jobson met with America's Cup Organizing Committee chief Tom Ehman last week to iron out details, and Jobson said he expects a formal announcement soon.

The developments, coupled with Cupholder Dennis Conner's continuing efforts to add to a $6 million war chest, bring to three the number of apparently strong defense syndicates. Contenders will begin vying for the right to defend the Cup in January 1992, just 15 months from now.

With 11 syndicates from a record nine countries also gearing up to begin trials to select a challenger at the same time, U.S. groups have their work cut out.

But the elimination of Klein's defense campaign and that of fellow Southern Californian Peter Isler, who also folded his tent for lack of funds last week, brings the number of U.S. groups to a more manageable level. "Three sounds right," said Jobson. "That's how many the New York Yacht Club used to have" when it oversaw a 132-year hold on the Cup from 1851 to 1983.

Ehman also sounded encouraged. He called the announcement by the Beach Boys Syndicate (the singing group is helping finance the campaign with a 125-concert tour) a "blockbuster," and welcomed the interest of Koch and Jobson.

"I think we're steadily closing the gap" between U.S. boats and the top foreign challengers, three of which already are in the water with boats and testing, Ehman said. "But we're still a long way behind the French, Italians, Japanese and New Zealanders."

Ehman announced last week the number of eligible Cup challengers had dropped to 11 as seven groups failed to make a deadline for posting $150,000 performance bonds. Three other groups, including one from the Soviet Union, asked for additional time and may still get in.