Pennant contenders always look for gold in unlikely places. Today the Baltimore Orioles found it.

Glenn Gulliver, the rookie third baseman with a penchant for getting on base but no great defensive expertise, turned three double plays, two of them sparklers, and seldom-used outfielder Jim Dwyer had a homer and a run-scoring single as Baltimore won its fifth straight game and 12th in the last 13 games.

The 5-2 victory over the Blue Jays wound up a three-game sweep here and the Orioles went home with their record improved to 15 games over .500, the best it's been all year. "When you get to 20 over you start thinking pennant," said Manager Earl Weaver. "Of course, we're thinking pennant now."

First-place Milwaukee maintained its five-game lead over the Orioles by beating Seattle, 7-3, last night. Second-place Boston defeated Oakland, 7-4, to remain a half-game ahead of Baltimore.

The Orioles' victory went to workhorse Dennis Martinez, who gave up seven hits in recording his 10th complete game of the season. Martinez has pitched 38 innings in the last 12 days, including two 10-inning performances and two nine-inning journeys. He won three of the games with no decision in the other to improve his record to 14-10.

The right-hander was less than overpowering early, but his teammates got him to a 4-0 lead in the second inning and it was more than enough.

Dwyer hit a 2-0 fast ball from loser Dave Stieb over the right field fence in blustery Exhibition Park for a 1-0 lead in the second. The homer evidently unnerved Stieb, who gave up a double to Rick Dempsey, a single to Rich Dauer and a two-run double to Al Bumbry, then threw two wild pitches that allowed Bumbry to score.

Toronto scored its runs in the second as Lloyd Moseby singled, Hosken Powell tripled (Bumbry falling head-over-teakettle as he retrieved it), and Powell came home on a sacrifice fly.

But Martinez, with a little help from his friends, pitched shutout ball thereafter. In the third, Gulliver stopped Rance Mulliniks' hard grounder to start one double play; he turned a high hopper into an inning-ending double play with the bases loaded in the fourth and he leaped high to grasp Garth Iorg's liner, then doubled Mulliniks off second to end the fifth.

Meantime, Dwyer made it 5-2 with the luckiest base hit of the week. With Cal Ripken on second with a double, Dwyer fought off "three of the toughest sliders I've ever seen" from Stieb and finally sent a meek grounder to first. Willie Upshaw was behind the bag to field it but it struck the base and bounded over Upshaw into right field, Ripken coming home.

The Orioles' 12-for-13 streak over the last two weeks has all been at the expense of lowly Toronto (6-0) and Texas (6-1). They will return home for three games against Minnesota, then the remainder of the pennant race will be head-to-head with tougher opposition: division mates New York, Cleveland, Detroit and first-place Milwaukee.

It worries Weaver not. "Those teams, particularly New York and Milwaukee, are ones we've done well against," he said.