Rookie outfielder Mike Young hit a bases-loaded home run and Dennis Martinez allowed one run in six innings yesterday as the Baltimore Orioles defeated the Minnesota Twins, 9-4, in a Miami exhibition.

Young's homer, his first of the spring, came off Jack Hobbs. The left-handed Hobbs, pitching only the sixth inning, also gave up a bases-empty homer to Ken Singleton and issued four walks. Switch hitter Singleton last hit a home run right-handed on Aug. 24, 1981.

The Orioles scored four times off Bryan Oelkers in the third inning. Rick Dempsey tripled, John Shelby singled and Dan Ford doubled. Gary Gaetti's error on Cal Ripken's bouncer and Eddie Murray's RBI grounder followed.

George Brett (.520) had seven RBI, with a two-run home run and a grand slam, both off Ross Baumgarten, and two singles as the Kansas City Royals beat Pittsburgh, 16-10, in Bradenton, Fla. Jason Thompson hit two homers, each with a man on base, for the Pirates . . .

Elsewhere in Florida:

Gary Redus hit a four-run homer in the Reds' 9-3 victory over Philadelphia. Mario Soto, set to pitch the opener April 4 in Cincinnati, struck out five in six innings of four-hit, one-run work . . . Montreal scored five times in the fifth inning and defeated Texas, 9-1. Steve Rogers permitted one bloop single in six innings; he will be the Expos' opening day pitcher an eighth straight season . . . Singles by Garth Iorg touched off two Toronto rallies in a 5-0 win over Boston . . .

Tony Bernazard's bad-hop single for the Chicago White Sox off first baseman George Hendrick's mitt in the eighth inning beat St. Louis, 1-0. LaMarr Hoyt held the Cardinals to four hits in seven innings . . . Claudell Washington cleared the fence twice and singled among 16 Atlanta hits that submerged Los Angeles, 12-1 . . . Tom Brookens' two-run homer carried Detroit over Houston, 5-4 . . .

The New York Yankees won their 10th of 13 exhibitions as Steve Kemp's two-run double launched a 9-1 rout of the Mets.

In the Cactus League: Mike Brown's second home run in two days helped California beat Cleveland, 3-1 . . . . Oakland used three doubles by Dwayne Murphy and a double and two-run homer by Dave Lopes to defeat Seattle, 9-3 . . . Milwaukee (10-2) beat San Diego, 7-2, as Marshall Edwards' three hits included an RBI triple . . . Max Venable's two-run, inside-the-park homer started San Francisco past the Chicago Cubs, 9-5.