The Pittsburgh Pirates completed their sensational World Series comeback last night in Baltimore, by defeating the Orioles, 4-1, in the seventh and deciding game of this year's fall classic.

The Bucs scored all the runs they needed in the top of the sixth inning when series star Willie Stargell followed Bill Robinson's single with a towering drive to leftfield for a two-run homer off the south-paw starter Scotty McGregor.

The lone Oriole run came in the bottom of the third when secondbaseman Rich Dauer tagged a Jim Bibby fastball for a bases-empty homerun.

The hulking righthander then settled back down to retire the side. Bibby gave manager Chuck Tanner one more strong inning before Manny Sanguillen was called on to pinchhit for him in the top of the fifth.

Bibby's replacement on the pitching mound, righthander Don Robinson, did not take long to get into a jam. The Birds' Doug DeCinces slashed a single up the middle to lead off the bottom of the fifth.

Dempsey and Dauer flied out but McGregor worked Robinson for a walk. Tanner had seen enough and called to the bullpen for veteran lefty Grant Jackson, who finished off the inning without allowing any damage to the Bucs' precarious lead.

The only other serious threat from the Orioles came in the bottom of the eighth when Lee May, pinchhitting for McGregor, drew a walk. The tiring Jackson then gave away another base on balls to Al Bumbry. Tanner removed Jackson and brought in Kent Tekulve.

Baltimore manager Earl Weaver sent Terry Crowley in to face the razor-thin reliever. Crowley hit into a force but succeeded in advancing both runners. Tekulve then tossed Ken Singleton four straight balls to load up the bases. Tekulve and the Pirates were banking on the slumping Eddie Murray to end the inning.

Murray, who had gone 0-20 since the second game of the series, gave the Bucs a scare when he sent ailing rightfielder Dave Parker to the warning track for the final out.

Despite Weaver's record-setting four pitching changes in the top of the ninth, the Pirates still added two insurance runs. Phil Garner sent Tim Stoddard's first pitch into left for a double off the wall. One out later Garner scored when Omar Moreno pushed a single up the middle off Stoddard's replacement, Mike Flanagan.

Moreno scored the final run three pitching changes later when Dennis Martiniz hit Robinson on the arm to force in the tally.

Tekulve finished off the Birds with ease in the bottom of the ninth, striking out Gary Roenicke and DeCinces, before Pat Kelly flied to Moreno to make the win official.

Stargell, the Pirates ageless slugger, capped off an amazing series, with a record-setting 25 total bases. He won the 1979 World Series Most Valuable Player Award.

Stargell scored the winning run in the seventh game of the 1971 World Series against the same Baltimore Orioles.