BOSTON (AP) _ They don't feel the sea spray, hoist sails or get a tan, but computer experts here feel as though they're part of the America's Cup races.

While yachts duel off San Diego, these competitors are battling for bragging rights for their computer laboratories, which helped make the yachts faster.

Experts at two high-tech companies, Digital Equipment Corp. and Hewlett- Packard Co., and the Massachusetts Institute of Technology are waiting to see if their work pays off.

''We're sitting here biting our nails,'' said Ralph Dormitzer, Digital's liaison to the America3 Foundation, which helped put the yacht America3 (America Cubed) in the water.

They used computers for an array of tasks, from plotting the effect of wind and ocean currents on various boat designs to devising a system for the boat navigator to speak to an on-board terminal.

''We have the fastest boat among the Americans,'' bragged Jerry Milgram, an MIT professor of ocean engineering who is design director for the America3 syndicate, headed by longtime acquaintance Bill Koch.

After a loss Thursday, America3 held a 3-1 lead over defending champ Dennis Conner in a best-of-13 series that will determine the U.S. representative in the finals.

It isn't surprising that computers are playing a big role in this year's race. Ever since Australia captured the trophy with a revolutionary winged- keel in 1983, sailing's premier event has become a showcase for technology as well as skippering talent.

Koch turned to MIT, his alma mater, as well as Massachusetts-based Digital.

Digital donated approximately $4 million worth of computers and services toward the America3 effort.

For some people at Digital, the races have become a mini-competition with rival computer maker Hewlett-Packard, which has provided equipment for Conner's team.

''It adds a bit of spice to this whole thing,'' Dormitzer said.

But at Hewlett-Packard, officials say the rivalry is strictly between the boats, not the companies.

David Perry, Hewlett-Packard's technical manager for America's Cup, noted that H-P machines were also used by America3 designers.

Much of the America3 work was done on Digital computers, including a high- powered mainframe at MIT that can run a special ''velocity prediction program'' developed by Milgram.

The program calculates yacht performance based on factors including the shape of the hull and sails, crew weight and the direction and wind speed.

Using computers, engineers could evaluate hundreds of different sail and boat design combinations without having to build them.