The Pittsburgh Pirates narrowed their deficit in the 1979 World Series to 3-2 by defeating the Baltimore Orioles, 7-1, at Three Rivers Stadium in Pittsburgh yesterday.

The two teams continue the series in Baltimore Tuesday night.

Neither team scored until the sixth inning, when Baltimore's Rich Dauer hit into an infield double play that scored Gary Roenicke, who had doubled and advanced to third on a single.

Pittsburgh retaliated in the bottom half of the inning, when two singles, a walk and two sacrifices produced two runs and a lead the Bues never relinquished.

The Pirates added two more in the seventh. Omar Moreno singled, and seampered to second on an errant pickoff attempt. Moments later, his sprint proved unnecessary when Tim Foli tripled to left-center. Foli then trotted home on a Dave Parker double, for a 4-1 lead.

Pittsburgh tallied its final three runs in the eighth, but the Orioles, stymied by Bert Blyleven's breaking balls, couldn't create any offense.

Jim Rooker, a surprise starter in the eyes of many, baffled the Baltimore bats for five innings, but ran out of gas in the sixth, in favor of Blyleven.

Making his first relief appearance in seven years, the Holland-born righthander doused the fire in the sixth and breezed through the final three innings to close the series margin to three games to two.

Baltimore Manager Earl Waver, whose use of pinchhitters played a large part in Saturday's come-from-behind, 9-6 victory, yesterday started his ace pitcher, Mike Flanagan.

In the early innings, Flanagan appeared unhittable but yielded to a pinchhitter with his team down 4-1. Tim Stoddard and Don Stanhouse finished for the Birds.

The Pirates have averaged more than 12 hits in each of five games, but have not capitalized with timely hitting. Erratic infield play has also hurt them.

Baltimore not only controls the home-field advantage, a 3-2 lead and stronger pitching, they also have historical precedent. Only three teams--the 1968 Tigers, 1958 Braves and 1925 Pirates--have ever recovered from a 3-1 deficit.

The Birds will throw star righthander Jim Palmer at Pittsburgh Tuesday, and go with Scott MacGregor if needed on Wednesday. The Pirates' staff is shaky--Blyleven is through for the series after today's outing, and Bruce Kison has not pitched well. Buc ace John Candelaria, despite an ailing back, may start the sixth game.