The Orioles reached the .500 mark for the first time since April 11 with a 3-1 victory over Toronto in the first game of a doubleheader at Memorial Stadium tonight.

Mike Flanagan allowed only five hits, but had to survive a shaky ninth inning to get the victory. Flanagan had no trouble until the ninth when pinch batter Anthony Johnson -a .125 hitter -bounced an infield single to third that scored Garth Iorg, who had led off the inning with a single.

It was the first time Flanagan had allowed Toronto a run since Sept. 21, 1980, a streak of 37 innings.

The victory gave the Orioles an 11-4 record in recent games and evened their season record at 22-22.

"I tried to throw too hard the last inning," Flanagan said afterward. "I got pumped up. I hadn't gone nine innings for a while.

"I pitched well. The curve ball was pretty good and I made good pitches with my fast ball."

Oriole Manager Earl Weaver came to the mound in the ninth, but left Flanagan in the game. "Mike pitched well," weaver said. "He was in charge all the way. But he got tired at the end and it was a tough decision whether to leave him in. fortunately, it worked out fine."

As for reaching .500, Weaver said, "It's a starting point."

The Orioles gave Flanagan a 2-0 lead in the first, with Ken Singleton hitting a sacrifice fly and Terry Crowley and RBI double. Crowley started at first base in place of Eddie Murray, whose left hand hurts too much when hitting against righthanders.

Baltimore's first three batters loaded the bases against Luis Leal. al Bbumbry started by singling and stealing second.

It looked as if the Blue Jays would get a break when Rich Dauer grounded sharply to Leal, who caught Bumbry off second. But the pitcher's throw was too high. Bumbry slid back safely on a close play and Dauer reached first on a fielder's choice.

Toronto Manager Bobby Cox, only 10 minutes into the game, was ejected for arguing about the call with second base umpire Vic Voltagio. After Leal walked John Lownenstein to fill the bases, Singleton scored Bumbry with a fly ball to right field.

Crowley's double to right made it 2-0 and, with only one out, it looked as if the Orioles were headed toward a big inning. But Lear intentionally walked Jim Dyer to face Joe Nolan, a .178 hitter. After running the count to 3-2, Nolan popped up meekly to center field for the second out, and Cal Ripken grounded to third, leaving three runners stranded.

Flanagan allowed only two hits through the first six innings -Damaso Garcia's two-out single in the third and Barry Bonnell's two-out infiled single in the sixth.

Leal, too, was impressive after the shaky first inning. He allowed harmless singles in the second, fourth and sixth innings.

Baltimore got an insurance run in the eighth, when Dwyer hit his third home run of the season--a line drive to right field--for a 3-0 Oriole lead.