As the sun set over Nassau harbor Friday, the 1981 Southern Ocean Racing Circuit ended. After three weeks and almost 1,000 miles of sailing, the last race was over and the 43-foot Louisiana Crude, a Class C boat from New Orleans, was declared fleet champion.

Many observers called this the toughest SORC ever. The weather favored smaller boats, and during back-to-back storms, the little guys repeatedly saved their times on their larger rivals.

"The goal was to win the SORC and then be chosen for the Admiral's Cup," said Dick Jennings, Chicago-based co-owner of Louisiana Crude.

Designer Doug Peterson had three of the top five finishers in the fleet.

Second place went to Burt Keenan in Acadia, a Freres 40. Also based in New Orleans, she was a Class D winner and is a strong contender for the Admiral's Cup.

Dennis Conner, America's Cup skipper, took third place overall and first place in Class B in Williwaw, a Peterson 48. When asked what distinguished this year's SORC from others, he replied: "The tremendous competition among the smaller boats." Williwaw is the largest boat competing for the Admiral's Cup and stands a good chance of being chosen.

The six-race series, one of the most prestigious and competitive in the world, ended well. The famed Miami-Nassau run, with 18-knot winds this year, gave this international offshore fleet its money's worth as it surfed through the night on a wild ride from Great Isaac's light to the welcoming blue waters of Nassau harbor.

The 73 competitors started from Miami at 2 p.m. last Monday, finishing here Tuesday afternoon. First over the line and in record time was Californian Jim Kilroy in his new 80-foot Kialoa, completing the 176-mile course n less than 13 hours to edge Bumblebee 4.

Two Class E boats dominated this second longest race in the series. Overall winner and second smallest in the fleet, Right On, owned by German skipper Karl von Wendt, finished the race in 22 hours. Third place went to Class E boat Thunderbird. Second fleet honors went to last year's over all winner, Class D Acadia.

Robin, which was sailed and designed by owner Ted Hood of Marblehead, Mass., was Class E leader and 10th in fleet before the Miami-Nassau race. During the tumultuous night sail, she lost her mast and put into Cat Cay.

The final race in the series started Friday off Nassau. Louisiana Crude won the Nassau Cup with Acadia and Williwaw close behind.

Class A was a fight to the finish between arch rivals Tenacious, owned by Ted Turner, and Alexanderia-based Running Tide, owned by Mr. and Mrs. Al Van Metre. The Van Metres benefited from a penalty that caused Turner to relinquish first place in Class A to Running Tide. Running Tide then beat Tenacious in the final race.

Class B was dominated by Dennis Conner, with second place going to Bravura, a freres 45 from Richmond, Calif. Another Freres 45, jack King's Merrythought, of Alexandria, Va. was a close third. She is also competing for the Admiral's Cup team.

Louisiana Crude, of course, won Class C. Locura, a 40-foot Soverel, was second, with Pat Malloy III's Intuition, a Peterson 42 from Sag Harbor, N.Y., a close third.

Class D was captured by Acadia.

When the Class E leader, Robin, was disabled, Celebation moved into first place. The cook 36 is sailed by Bruce and Pat Clark.

Three Washington, D.C., area boats, Merrythought, running Tide and Bill McAtteer's Immigrant from Annapolis, won the team race, a new adition to the SORC.

Interest now turns to the 25 boats competing for three slots on the U.S. Admiral's Cup team. The selections will be made after the last trail race Sunday. The winners will represent the U.S. in England this summer.