AMERICA’S CUP ’92 : Stars & Stripes Fading; Nippon Team On Rise : Sailing: Dennis Conner’s boat towed back to port after the mast breaks.

If a mast falls in the America’s Cup, does anybody hear it?

If it’s Dennis Conner’s mast, the crash is heard ‘round the world.

His hopes for defending the America’s Cup already were fading under America 3 rival Bill Koch’s overwhelming resources Tuesday when catastrophe struck at the first, windward mark.

Trailing Koch’s newer boat, America 3 , by 35 seconds, or about six boat lengths, Conner was halfway around the buoy in about 12 knots of wind when the block, or pulley, on the starboard running backstay broke with a bang. The $500,000, 110-foot spar snapped a third of the way up, toppled forward, cracked again as it struck the bow and splashed into the water.

Conner, struck on the head and back by flying hardware, then sat calmly on the rail as crewmen went into the water to retrieve the sails. With the mast still hanging off the bow, the midnight-blue Stars & Stripes had to be towed backward into port.

Even as Conner’s star descended on the day, Japan’s sun continued to rise in the challenger trials. Skipper Chris Dickson’s Nippon, a five-second winner over powerhouse Il Moro on Sunday, survived a threatening backstay problem to defeat another member of the apparent Final Four, Ville de Paris, by 46 seconds. That left Nippon tied for first place with New Zealand, whom they’ll meet Saturday.

It was only the fifth race for Stars & Stripes’ mast, which had been installed for this third round of the defender trials. Scheduled to race America 3’s older Defiant today, the crew planned to work overnight to re-install their older, original mast, heavier and less efficient.

They also will have to return to their older, lighter--and less efficient--mainsail. The better one was shredded, further damaging Conner’s chances for catching up to Koch, let alone reaching the May finals.

“If we’re looking for a bright side,” Conner said, “the boat was going better than it has against America 3 , and if we keep on target we’re still gonna be all right. Our guys are not gonna let a broken mast bother ‘em. We’ve been through worse.”

Conner said he put the incident in perspective for the crew by saying, “Imagine having something that costs 10 times the price of your house go up in flames without having any insurance.”

The mast probably will be repaired and used again, he said.

The problem was the $2,000 block. The port runner was eased because Stars & Stripes was on port tack approaching the mark, and it was just a matter of letting out the main to bear away downwind.

But when Conner turned and the wind caught the backside of the sail and pushed the mast forward, the block on the starboard runner broke and the mast was left with no support. Five seconds later it was in the water.

The genoa headsail also was dunked, as was the spinnaker the crew was about to raise, but the spinnaker still was wrapped in a tight roll and both sails were salvaged.

It was the sixth mast to collapse on one of the new International America’s Cup Class boats but the first in this year’s trials. New Zealand, Il Moro di Venezia, Nippon and America 3(twice) suffered similar mishaps. Koch had predicted 10 would fall before it’s all over.

And if anyone thinks Koch will lend Conner a spare mast for the sake of keeping him competitive, they can think again.

“Having lost a couple of masts . . . we can certainly understand the feeling at the Team Dennis Conner camp,” read an unattributed statement issued by America 3 . “Presently, we have only one spare mast between our two boats and so we can empathize with their situation.”

As the wind built to 19 knots, other boats had trouble, as well.

When the Nippon crew suspected its backstay block was about to break, tactician Erle Williams climbed out on the end of the boom for 10 1/2 minutes of one reaching leg to repair it, swapping jokes with Dickson and navigator John Cutler as he worked.

Challenge Australia pulled out while trailing in its race against Spain when its mainsail tore apart, and Spirit of Australia sailed the last third of its race against New Zealand with a broken rudder shaft, losing by 8:10.

Il Moro won a relatively uneventful race from Sweden’s Tre Kronor by 4:47.

Marc Bouet steered Ville de Paris to a strong start against Nippon, but skipper Marc Pajot couldn’t hold off Nippon’s speed.