At least 10 yachtsmen have been killed, seven reported missing and more than 100 rescued from a rough sea off the southwestern coast of England after 70-mile-an-hour winds turned Britain's most important ocean yacht race into an international tragedy yesterday.

Rescue craft still were searching the sea from the southwestern tip of England to the southern coast of Ireland this morning. They sought missing yachts and crewmen who were caught in the surprise storm during the Biennial Fastnet Race from Cowes, on the Isle of Wight off England's southern coast, to the Fastnet Rock Lighthouse off Ireland's southern coast and back to the port of Plymouth in southwestern England. The race is one part of Admiral's Cup international competition.

Many of the 114 yachtsmen who were rescued from the sea had been tossing around in life rafts for hours. Others had to go overboard from their crippled yachts to be picked up so that rescue helicopters could avoid the sailing crafts' tall masts.

Eight of the 10 known dead came from five British yachts, some of which sank.The other two dead, still unidentified this morning, were from the American yacht Ariadne, which also was believed to have sunk. The seven men still missing at sea and feared drowned were from these same yachts.

Of the 330 yachts that began the 605-mile race from Cowes on Saturday, 25 have sunk or are feared lost at sea, according to the Royal Ocean Racing Club, sponsor of the prestigious and challenging race, run every other year since 1925.

Dozens of other disabled yachts have been towed to Irish and British ports, and the rest are scattered in the Atlantic and various harbors, safe but still unaccounted for. Some of the yachts are still finishing the race but to keep the radio channels clear for boats in trouble, they have not contacted the authorities.

One of the best known American yachts in the race, Tenacious, owned and captained by famed Atlanta yachtsman Ted Turner, made port safely early this morning. Turner also is the owner of the Atlanta Braves baseball team and the Atlanta Hawks basketball team. Last week, he guided Tenacious to victory in two other races off the southern English coast, including the prestigious Britannia Cup, during the Cowes Week Regatta, which was climaxed by the start of the Fastnet race Saturday.

Turner, best known in yachting for winning the last challenge for the America's Cup in September 1977, at the helm of Courageous, also had set the record time for the Fastnet Race when he won it in 1971, in just more than 19 hours. That record was broken yesterday when this year's winner, the 77-foot Condor from Bermuda, took advantage of the howling winds to finish in less than 72 hours, followed closely by the 79-foot American yacht Kialoa.

A U.S. Naval academy entry in the Fastnet Race, the 54-foot Alliance, with a crew of eight Annapolis midshipmen and four others, was among the boats still unaccounted for this morning.

Among the yachts reported to be returning safely to port was Morning Cloud, owned and captained by former British Prime Minister Edward Heath, a respected ocean racer. After Morning Cloud's rudder broke during the storm, Heath had it repaired in an Irish port and sailed for Falmouth on the southern coast of England, where he is expected today.

Morning Cloud was part of a three-yacht British team, of which Heath was captain, in the Admiral's Cup competition among 54 yachts from 18 nations.The Fastnet Race, which other yachts are free to join, is the last, most difficult and highest-scoring leg of the international competition.

Peter Jay, the former British ambassador to the United States and son-in-law of former British prime minister James Callaghan, was helped by a rescue boat into a harbor in County Cork, Ireland, after his catamaran ran into difficulty in the stormy seas yesterday. Jay, who has a summer house in County Cork, was not injured.

A British lifeboat from St. Ives in southwest England battled the towering waves for nearly 10 hours to rescue French yachtsman Marc Gillemot, who was competing in a single-handed race from France to Ireland and back. Another Frenchman was swept off a pleasure yacht while sailing from Ireland to Penzance, and was feared lost at sea.

The storm blew through most of the British Isles, causing widespread property damage and killing at least three people on land who were struck by falling trees and rocks. The Severn Bridge between England and Wales was closed after the wind toppled a camper van.

Although relatively high winds of "near gale force" were being predicted by midday Monday -- yachts in the Fastnet Race were counting on them to improve their times -- the ferocity of the storm was unexpected.

The Royal Ocean Racing Club is to investigate the circumstances of the tragedy.

"Naturally, we are all horrified that this has happened," said an official of the club. "A weather pattern developed virtually without any warning. It built up extremely rapidly and was so severe it could be called freak weather," he said.

Some yachting experts here, however, questioned whether too many smaller boats had been allowed to compete in the Fastnet Race, considered difficult in the best of weather. Most of the yachts in the worst trouble yesterday were smaller boats; the larger craft with top-flight racing crews apparently rode out the storm.

Rescue workers from the Royal Navy and Air Force and the famed British Volunteer lifeboat service told reporters they had seen nothing like it before.

"There were dozens of empty yachts just drifting around," said Navy Airman Alf Tupper. "It was strange -- millions of pounds' worth of ships and, from what we could see, nobody on board. Spooky."

"They were the worst seas I have ever been in," said David Bootham of Paris, who was stranded on the rudderless Magic for 10 hours until its crew was rescued. "We were just wallowing in the high seas. "We were ordered to batten ourselves down and hope. That was the worst time -- just cramped together, wondering whether anyone would find us."

"It was not so much the wind as it was the mountainous seas," recalled Englishman Arthur Moss, who was rescued from his crippled yacht Camargue. "The boat turned turtle a couple of times and then righted itself again, I think by sheer wave power. They were just enormous. My clothes were torn and my wristwatch just disappeared. It must have been wrenched off."

Carmague crewmen Frank Worley described how he was forced to jump into the heaving sea and struggle to stay afloat until he was hoisted to safety by a rescue helicopter.

"That was the hardes part of all," he said.