SAN DIEGO -- The breeze was dying on the Pacific outside the harbor entrance, but here in San Diego Bay a freshet came dancing across the water on cats'-paws.

US II, first of the new International America's Cup Class boats to fly the American flag and first of any to hit the water here, where 1992 Cup trials will begin in less than a year, heeled to the breeze and gathered speed.

A crew member spotted a familiar shape up ahead. "There's Stars & Stripes," he said, pointing toward the city skyline at the curve of a Kevlar sail over a gray-blue hull.

US II sped ahead, gaining ground on the lumbering, five-year-old 12-meter that was part of Dennis Conner's successful 1986-87 Cup campaign in Australia. Soon the two boats were side by side, clipping along. Skipper Bill Koch twitched the new boat's wheel, bringing her up on the wind. Stars & Stripes' helmsman did likewise. The race was on.

But it was no contest. New blew old away in a trice, and for the folks on Stars & Stripes there was nothing left but to cheer and wave on the big, white intruder from the future.

That chance encounter last week confirmed, if anyone had lingering doubts, that a new age has dawned for the America's Cup -- an age of speed, power, performance and grace. After 30 years of competition in the majestic but antiquated 12-meter class, now nearly a century old, the Cup will take a leap forward this year into a world of space-age, baked-carbon-fiber hulls, computerized sail shapes, titanium fittings and massive, powerful, 100-foot-tall rigs.

"I've watched US II sailing," said Bill Trenkle, Conner's operations manager and a sail trimmer on 12-meters for more than a decade. "It's more than worthy. It's elegant and very high-tech.

"I used to think 12-meters were beautiful," said Trenkle, "but seeing a new ACC boat reaching along at 12 knots in six knots of breeze -- wow!"

"Oh, it's good boat," said French skipper Marc Pajot of the new Cup class. "The problem now is learning how to sail it, make it faster." Pajot sailed

US II in the Mediterranean as France I, before his French syndicate sold it to Koch's team to use as a training vessel while both syndicates build improved boats for Cup races, which will start Jan. 10.

The new class, which all Cup aspirants have agreed to sail in at the 1992 regatta, was hatched from the wreckage of the 1988 defense, when Cupholder Conner went to sea in a little catamaran and obliterated the hostile challenge of Michael Fay and his 132-foot-long behemoth, New Zealand.

That preposterous mismatch nearly sank the Cup in the minds of a confused public, which had grown to love the event as a tense showdown between the closely matched, if anachronistic, 12-meter sloops.

While the '88 debacle was played out on the water, a group of top yacht designers from around the world met to fashion a new Cup class that would be acceptable to all, yet lively enough in San Diego's light winds to create some excitement.

The agreed-upon solution was the America's Cup Class, a formula for an overpowered, superlight, expensive 75-footer that 14 syndicates from 11 countries, including two potential U.S. defense groups, are frantically working to tame.

"What I noticed first was the responsiveness," said Koch, who took his first sail on US II this month while trying out aspiring crewmembers for his America 3 Cup team. "You turn the wheel and the bow comes right up. There's no delay. She's very quick."

Small wonder. At about 33,000 pounds, US II is less than two-thirds the weight of an old, aluminum 12-meter, yet she's 10 feet longer and wider at the beam. Her 100-foot-plus, carbon-fiber mast supports 50 percent more sail than a 12-meter, and when the immense, 4,500-square-foot spinnaker is set from the masthead, US II all but disappears under a cloud of filmy sail.

When you cut the weight that drastically and increase sail area that dramatically, the net result is speed, speed, speed. America's Cup Class boats are expected to shoot along at more than 15 knots in 10 knots of wind on favorable points of sail. If that sounds improbable, it's the phenomenon of modern racing yacht design -- a boat that sails faster than the wind that propels it, effectively going so fast it creates its own wind.

Such advances do not come cheaply, of course. Building hulls and spars from featherweight carbon-fiber composites instead of clunky aluminum dramatically increases construction costs. Masts alone will fetch $600,000 apiece, Koch said, and overall cost for an ACC boat will range up to

$3 million, four or five times the cost of an old 12-meter.

Many longtime Cup observers feared the increased expense would drive potential competitors away, but even with the short time frame of the '92 Cup, which will begin just 1 1/2 years after the 1988 results were finally upheld in court, the field has more challenging nations than ever.

The question now is whether yacht designers from around the globe can produce a field of reasonably competitive boats, working on a short timetable within the puzzling parameters of a brand new class.

The worst worry for Tom Ehman, executive director of the America's Cup Organizing Committee, which oversees the event, is that some clever designer will find a loophole somewhere in the new class rule and come up with a breakthrough design that blows everyone else in the field away.

"All I want," said Ehman, "is a seventh race" in the best-of-seven final series between the top foreign challenger and the top U.S. defender. "Give me a seventh race and I'll give you the best regatta ever."

It would be a refreshing change. "There's still a bad taste in everyone's mouth" from the '88 regatta, said Noah Rosenblatt, who does a yachting show on a local radio station.

"This is either going to be the best America's Cup ever or the last one," said Ernie Taylor, who heads the Challenger of Record Committee, representing 12 challengers from 10 nations who have signed up to compete. "The possibilities are enormous."