Dennis Leonard pitched a three-hitter in his first start in almost three years and Jorge Orta's pinch double in the eighth inning allowed the Royals to beat the Toronto Blue Jays, 1-0, yesterday in Kansas City, Mo.

Leonard struck out three and did not give up a walk, retiring 18 batters in a row before Tony Fernandez singled with two out in the ninth. It was his first major league start since the three-time 20-game winner snapped a tendon beneath his left knee while throwing a pitch against Baltimore on May 28, 1983. His long rehabilitation included four operations. It was the 22nd shutout of Leonard's career.

"I couldn't ask for more. It's a great feeling," Leonard, 34, said. "This makes all the work worthwhile. It's my greatest thrill in baseball."

Leonard was the winningest right-hander in baseball from 1975 to 1981, recording 120 victories before being sidelined by broken fingers on his right hand when hit by a line drive by Texas' Buddy Bell May 21, 1982.

Royals Manager Dick Howser termed the drama of Leonard's no-walk, three-strikeout performance "unbelievable. It's quite a story. It's remarkable. The feeling that everybody in the dugout had was not unlike the feeling a team gets in the seventh game of the World Series . . . I don't usually get caught up in the emotion of these things, but I did today."

Toronto's Jim Acker (0-1) retired the first 11 batters and gave up only three hits until Jim Sundberg singled with two out in the eighth. Orta then hit a pitch from reliever Don Gordon over the head of Jesse Barfield in right field to score pinch runner Buddy Biancalana.

Royals left fielder Lonnie Smith sprained his left ankle when he fell while making a diving catch of a ball hit by Willie Upshaw in the seventh. He will be sidelined at least 10 days.

*Angels 9, A's 3: Bob Boone and Reggie Jackson homered to spoil Joaquin Andujar's American League debut as visiting California won behind the six-hit pitching of Kirk McCaskill and Donnie Moore.

Andujar's start was his first since serving a five-day suspension for his temper tantrum involving umpire Don Denkinger in the seventh game of the 1985 World Series, which Andujar's St. Louis Cardinals lost to Kansas City. Denkinger was behind the plate for Andujar's AL debut and called his first pitch a strike, much to the delight of the 35,434 fans.

But Andujar lasted only four innings plus two batters in the fifth. He gave up at least one run in every inning. Jackson hit his 533rd career homer leading off the fifth, leaving him one shy of Jimmie Foxx for seventh place on the all-time home run list.

*Indians 6, Tigers 2: Joe Carter, Brook Jacoby and Pat Tabler homered and Ernie Camacho pitched out of a bases-loaded, none-out jam in the eighth inning for Cleveland at home.

Carter's two-run homer, his second of the season, highlighted a three-run first inning against loser Jack Morris (1-1), who has allowed six homers in two appearances this season. Morris walked four batters in the first inning, throwing 48 pitches. Julio Franco drew a one-out walk before Carter's homer. Morris then walked three straight and threw a wild pitch that let Jacoby score.

Cleveland starter Ken Schrom (2-0) blanked Detroit on four hits over the first six innings.

*Mariners 10, Twins 4: Danny Tartabull drove in three runs with a single and a two-run homer and Gorman Thomas capped a five-run seventh inning with a two-run homer, leading Seattle in Minneapolis.

*White Sox 3, Red Sox 1: Reid Nichols drove in three runs and Tom Seaver (1-1) pitched seven innings to earn the 305th victory of his career, giving Chicago, at home, its first win after four losses.

*Yankees 7, Brewers 3: In New York, Butch Wynegar and Dave Winfield homered in a four-run fifth inning against Milwaukee's Ted Higuera.