Ken Singleton's 19th home run in the top of the ninth inning tonight completed the Baltimore Orioles' 7-3 triumph over the Oakland A's.

The victory, the Orioles' second straight after losing the first five on their current road trip, pushed Baltimore's American League East lead to three games over the Boston Red Sox, a 6-0 loser tonight to California.

Mike Flanagan picked up his 11th victory in 17 decisions for the Orioles, but not before Oakland rallied in the bottom of the eighth to narrow the Baltimore lead to 6-3. $

Flanagan was solid, if not overwhelming, in scattering nine hits over 7 2/3 innings and raising his team-leading strikeout total to 82. After the A's pulled within three in the eighth, Don Stanhouse relieved and shut off further threats.

John Lowenstein led off with a single and went to second on a wild pitch to Doug DeCinces, who then walked.

After another wild pitch advanced both runners, Rich Dauer singled, scoring Lowenstein, and Rick Dempsey doubled over the head of catcher Mike Heath, playing left field. AlBumbry's sacrifice fly and Kiko Garcia's single, both off reliever Jim Todd, closed the inning with the Orioles up 4-0.

In the third, Lowenstein reached on a fielder's choice, stole second and scored on Dempsey's single to left. DeCinces, who reached base when A's third baseman Dave Chalk bobbled his grounder, scored when Chalk did likewise with Bumbry's, giving the Birds a six-run cushion.

The A's, whose scoring ability is little more than a rumor, mounted nothing even resembling a threat off Flanagan until the fifth inning when singles by Rob Picciolo and Ricky Henderson back-to-back were nullified by a double play off Chalk's bat.

Flanagan looked shutout-strong until, with two out in the sixth, Jim Essian sent his fifth home run 345 feet into the left field seats to make it a 6-1 matter.

Craig Minetto came on to start the sixth inning in relief of Todd and retired 11 straight batters, which seemed to be a terrible waste of fine pitching until the A's made things serious in the eighth with a single by Heath, a walk to Essian and a two-run triple to the base of the wall by Tony Armas.

This brought the call for Stanhouse, who worked for along fly ball out of pinch hitter Wayne Gross to end the inning.

Minetto's effort was marred further with two out in the ninth, when Singleton sent his 19th home run into the emptiness of the left field stands to make it 7-3. CAPTION: Picture, Pat Kelley of Orioles breaks up double play by taking A's shortstop Rob Picciolo out of play in third inning. AP