The case of the Toronto sea gull came to a swift conclusion when a prosecutor withdrew the cruelty-to-animals charge against New York Yankee outfielder Dave Winfield for fear of "adding to errors already made."

Winfield killed a sea gull, apparently accidentally, with a thrown ball in the fifth inning of a game between the Yankees and host Blue Jays Aug. 4. After the contest, a Toronto policeman arrested the surprised outfielder and charged him with cruelty to animals.

During a minute-long hearing in Ontario Provincial Court, prosecutor Norm Matusiak wore a plastic sea gull lapel pin. "I called it the Jonathan Livingston Case," Matusiak said.

In dismissing the charge, Judge Jack Cannon said, "As Hamlet said on Elsinore, 'The rest is silence.' " . . .

Manager John McNamara, who has watched his California Angels slide from first place to fourth in the American League West, has been rehired for the 1984 season, team owner Gene Autry announced.

The Angels led the AL West through most of the first half of the season, but slipped badly after the All-Star break and trailed the first-place Chicago White Sox by eight games going into last night's games.

"Despite an abnormal number of injuries to key players, we feel John has done a good job in handling the team," Autry said in a prepared statement.

Donell Nixon of the Bakersfield (Calif.) Mariners stole two bases Thursday night to tie the all-time minor league single-season stolen base record of 123.

Nixon, 21, a third baseman from Evergreen, N.C., who was the Seattle Mariners' 10th-round selection in the June 1980 free agent draft, tied the record set by Jeff Stone of Spartanburg of the South Atlantic League in 1981. Ahead lies the professional record of 130 set by Rickey Henderson of the Oakland A's last season.