Battle to decide America's Cup challenger a study in contrasts. New Zealand's nimble boat sails against straight-line US entry

In this week's down under ``Spar Wars,'' all eyes are on Dennis Conner, the San Diego skipper who lost the America's Cup to the Australians three years ago in Newport, R.I., and today is the United States' only hope of ``yanking'' the ``Auld Mug'' back home. Stars & Stripes, the sleek new yacht skippered by Conner, recognized as the world's most experienced 12-meter yacht helmsman, has already outperformed all but one other prospective challenger in reaching the finals of the Luis Vuitton Cup elimination series. The competition, which has lasted three months, is taking place in a treacherous patch of the Indian Ocean off the coast of Perth, in Western Australia.

Now it has reached the showdown stage, with Stars & Stripes, representing the San Diego Yacht Club, going against New Zealand, skippered by young Chris Dickson of Auckland's Royal New Zealand Yacht Squadron. Dickson, the best rookie helmsman in America's Cup history, sails a revolutionary and speedy fiberglass boat nicknamed the ``Plastic Fantastic.'' But it was Conner who got the first jump, winning Tuesday's opener of the best-of-seven series that will determine the challenger for the actual cup races against Australia beginning Jan. 31.

Meanwhile, the Australian yacht defending the cup for the Royal Perth Yacht Club is being decided in the best-of-nine Sir Thomas Lipton Cup series. Kookaburra III, skippered by Iain Murray and owned by Perth department store magnate Kevin Parry, sails the 24.1-mile, eight-leg America's Cup course against Australia IV, skippered by Colin Beashel and owned by Alan Bond, the boisterous millionaire whose Australia II, the ``Wonder From Down Under,'' wrenched the ``Auld Mug'' from Conner during the Newport races in 1983.

The America's Cup races which began here in early October have attracted the fastest 12-meter fleet in yachting history, a field of 19 challenging yachts from six nations. Among the competitors were six American boats representing yacht clubs from San Francisco to Chicago, New York to Newport, Calif. America II, the flagship of a two-year, $20 million campaign by the New York Yacht Club, which until 1983 had successfully defended the cup for 132 years - the longest winning streak in sports history - was surprisingly bumped out in December, failing even to reach the semifinals.

That Conner has come this far startles no one. The big news of the series, however, has been the astounding success of New Zealand, a dark-horse yacht marking that country's first appearance in America's Cup competition.

The Kiwis chalked up a 37-1 record in the elimination trials (they lost once in October to Stars & Stripes, but defeated Conner on two other occasions). Then in the semifinals New Zealand ground French Kiss (one of France's two entries) into fine p^at'e. In America's Cup timing, two minutes is an eternity, and New Zealand shut out the French by winning four straight races with better than two-minute margins in all but the final race.

Going into the finals, however, many observers suspected that New Zealand's performance curve may have peaked too early. They pointed out that back in October the Kiwis were beating the French by the same margin, and that since then their boat speed has not improved significantly.

Conner's history in Fremantle is the flip side. He faltered in the November and December trials and squeaked into the semifinal with a 27-7 record. In the semifinals, however, he changed his tune. Against San Francisco's dual-ruddered yacht USA, Conner's Stars & Stripes unleashed hidden speed and easily won four straight races in the best-of-seven series.

Tom Blackaller, USA skipper and longtime Conner rival, said Stars & Stripes' newfound speed was ``baffling.'' He mused that Conner's success factor must have been the addition of those ``funny, stubby little keel wings that look like they were designed by his daughter.''

Whatever Conner's ``secret weapon'' may be, he has no intention of divulging it. The fact is that Conner did clock his fastest time on the America's Cup course during the semifinals against USA, and that time was a full eight minutes faster than New Zealand's elapsed time against French Kiss.

Those sorts of comparisons can be deceptiave. Dickson sails a small, light, and nimble boat: His strategy is to wear down his opponents with time-consuming tacking duels. Conner's large Stars & Stripes goes for straight-line speed. Generally the object in America's Cup match racing is to win the start, stay ahead, and foul your opponent's wind, don't let him pass, and win as slowly as possible.

When a yacht jumps out too far ahead, it risks losing control over its opponent, which then can slip away, pick up a favorable wind shift, and sneak past the finishing line first, as Australia II did in her dramatic victory in Newport over Conner's Liberty three years ago.

As this week's racing progresses, one can expect Dickson to engage Conner, try to take the lead, and ``cover'' him. Conner will do everything to avoid traditional pre-start maneuvering and keep from getting entangled with Dickson.

At the moment, the winner of the Stars & Stripes vs. New Zealand battle is the odds-on favorite to beat the Australian defender. Even Ben Lexcen is worried. Lexcen, who designed the revolutionary ``winged keel'' largely responsible for Australia II's victory over the Americans in 1983, has warned that unless both Kookaburra III and Australia IV improve their performance in the next few weeks, their prospects of keeping the cup in Australia are most slim.

Australia IV's latest weapon is a balloon jib sail, jokingly called a ``gennakker'' because it looks like a hybrid of a genoa and spinnaker sail used to gather speed on downwind legs. The Bond syndicate is also rumored to be toying with a radical new bronze keel with stainless-steel wing tips inspired by the design of the unsuccessful British challenger, White Crusader. Quotable quote

Michael Cooper of the Los Angeles Lakers on the pleasures of sinking three-point shots on the road: ``It's a noise buster. When you bury one, ooooh, they go dead silent.''